$43+ Cheap flights from Colorado to Illinois
This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 4/3. Fares are subject to change and may not be available on all flights or dates of travel.
DEN — ORD
Apr 18 — Apr 251
Round-trip
1 adult, Economy
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Cheapest flights from Colorado to IllinoisExplore the most affordable flight options available from Colorado to Illinois. Find the lowest fares from popular airlines and budget airlines, with prices last updated on March 19, 2026.
Explore the most affordable flight options available from Colorado to Illinois. Find the lowest fares from popular airlines and budget airlines, with prices last updated on March 19, 2026.
This Cheapflightsfares deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 4/66:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/15![Frontier logo]()
$105
This Frontier deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Fri 4/108:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/14![Frontier logo]()
$106
This Kiwi.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/16:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 4/68:19 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/18![Frontier logo]()
$107
This Kiwi.com deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/304:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Mon 5/48:17 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$111
This Frontier deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/14![Frontier logo]()
$112
This Priceline deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 4/264:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Mon 4/278:17 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$118
This Frontier deal was found by Cheapflights users on 3/13. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 5/14:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Mon 5/48:17 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/13![Frontier logo]()
$120
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 4/106:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 4/138:19 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$121
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/16:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$127
This Cheapflightsfares deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 5/84:15 pm
DEN
- STL
Nonstop2h 08m
Frontier
Mon 5/118:08 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/18![Frontier logo]()
$129
This Frontier deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 6/14:15 pm
DEN
- STL
Nonstop2h 08m
Frontier
Wed 6/38:08 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/15![Frontier logo]()
$130
This Cheapflightsfares deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 3/279:19 pm
DEN
- ORD
Nonstop2h 38m
Frontier
Wed 4/13:29 pm
ORD
- DEN
Nonstop3h 08m
Frontier
Deal found 3/16![Frontier logo]()
$174
Best flights from Colorado to IllinoisDiscover carefully curated flight deals from Colorado to Illinois that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated March 19, 2026.
Discover carefully curated flight deals from Colorado to Illinois that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated March 19, 2026.
This Southwest deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 4/186:30 am
DEN
- MDW
Nonstop2h 20m
Southwest
Sat 4/185:30 pm
MDW
- DEN
Nonstop2h 40m
Southwest
Deal found 3/14![Southwest logo]()
$215
This United Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 4/214:35 pm
DEN
- ORD
Nonstop2h 39m
United Airlines
Sun 4/2611:03 pm
ORD
- DEN
Nonstop2h 55m
United Airlines
Deal found 3/18![United Airlines logo]()
$223
This Delta deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/151:14 pm
COS
- STL
1 stop7h 05m
Delta
Tue 4/219:59 am
STL
- COS
2 stops13h 14m
Delta
Deal found 3/17![Delta logo]()
$226
This CheapOair deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 6/123:57 pm
DEN
- STL
Nonstop2h 16m
Frontier
Sun 6/146:40 pm
STL
- DEN
1 stop18h 57m
Frontier
Deal found 3/18![Frontier logo]()
$260
This American Airlines deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 5/112:41 pm
DRO
- ORD
1 stop8h 19m
American Airlines
Fri 5/83:00 pm
ORD
- DRO
1 stop7h 43m
American Airlines
Deal found 3/14![American Airlines logo]()
$268
This Southwest deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 4/1810:50 am
DEN
- ORD
Nonstop2h 30m
Southwest
Mon 4/206:15 pm
ORD
- DEN
Nonstop2h 50m
Southwest
Deal found 3/16![Southwest logo]()
$218
This Southwest deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 5/276:35 am
DEN
- MDW
Nonstop2h 20m
Southwest
Sat 5/3010:30 am
MDW
- DEN
1 stop4h 45m
Southwest
Deal found 3/16![Southwest logo]()
$218
This Delta deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/2212:35 am
DEN
- MDW
1 stop7h 12m
Delta
Mon 4/275:21 pm
MDW
- DEN
1 stop8h 15m
Delta
Deal found 3/17![Delta logo]()
$241
This United Airlines deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 7/177:40 pm
DEN
- ORD
Nonstop2h 39m
United Airlines
Sun 7/265:00 am
ORD
- DEN
Nonstop2h 42m
United Airlines
Deal found 3/17![United Airlines logo]()
$245
This Southwest deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/308:20 pm
DEN
- MDW
Nonstop2h 20m
Southwest
Thu 5/79:35 pm
MDW
- DEN
Nonstop2h 40m
Southwest
Deal found 3/16![Southwest logo]()
$221
This United Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 7/179:05 pm
DEN
- ORD
Nonstop2h 39m
United Airlines
Sun 7/195:00 am
ORD
- DEN
Nonstop2h 42m
United Airlines
Deal found 3/18![United Airlines logo]()
$245
This Delta deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 5/201:55 pm
COS
- ORD
1 stop6h 58m
Delta
Tue 6/25:30 am
ORD
- COS
1 stop8h 18m
Delta
Deal found 3/14![Delta logo]()
$261
This American Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/295:04 pm
DRO
- ORD
1 stop5h 44m
American Airlines
Sat 5/26:57 am
ORD
- DRO
1 stop6h 14m
American Airlines
Deal found 3/18![American Airlines logo]()
$288
This United Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 8/147:05 pm
DEN
- ORD
Nonstop2h 36m
United Airlines
Sun 8/165:00 am
ORD
- DEN
Nonstop2h 39m
United Airlines
Deal found 3/18![United Airlines logo]()
$245
This Southwest deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/36:35 am
DEN
- MDW
Nonstop2h 20m
Southwest
Fri 6/125:15 am
MDW
- DEN
Nonstop2h 35m
Southwest
Deal found 3/16![Southwest logo]()
$223
This Delta deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/96:12 pm
DEN
- STL
1 stop4h 13m
Delta
Sat 4/116:00 am
STL
- DEN
1 stop6h 55m
Delta
Deal found 3/16![Delta logo]()
$261
This Southwest deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/911:40 am
DEN
- MDW
1 stop4h 35m
Southwest
Mon 5/119:35 pm
MDW
- DEN
Nonstop2h 40m
Southwest
Deal found 3/16![Southwest logo]()
$224
This American Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/212:42 pm
MTJ
- ORD
1 stop6h 15m
American Airlines
Sun 5/36:04 am
ORD
- MTJ
1 stop6h 54m
American Airlines
Deal found 3/18![American Airlines logo]()
$309
This Southwest deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 4/76:15 am
DEN
- ORD
1 stop5h 35m
Southwest
Wed 4/811:55 am
ORD
- DEN
2 stops8h 30m
Southwest
Deal found 3/17![Southwest logo]()
$226
This United Airlines deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 4/105:55 pm
DEN
- PIA
Nonstop2h 24m
United Airlines
Mon 4/137:43 pm
PIA
- DEN
1 stop5h 16m
United Airlines
Deal found 3/14![United Airlines logo]()
$279
This American Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 4/57:00 am
DEN
- PIA
1 stop4h 47m
American Airlines
Sat 4/115:40 pm
PIA
- DEN
1 stop7h 05m
American Airlines
Deal found 3/18![American Airlines logo]()
$309
This Delta deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 5/191:55 pm
COS
- ORD
1 stop7h 32m
Delta
Wed 5/2711:09 am
ORD
- COS
2 stops11h 18m
Delta
Deal found 3/15![Delta logo]()
$305
This United Airlines deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:10 pm
DEN
- MLI
Nonstop2h 22m
United Airlines
Sun 4/127:34 pm
MLI
- DEN
1 stop6h 24m
United Airlines
Deal found 3/17![United Airlines logo]()
$279
This Southwest deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/96:35 am
DEN
- MDW
Nonstop2h 20m
Southwest
Thu 4/93:35 pm
MDW
- DEN
1 stop5h 25m
Southwest
Deal found 3/15![Southwest logo]()
$231
This American Airlines deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 9/95:07 pm
DRO
- ORD
1 stop5h 59m
American Airlines
Mon 9/145:00 am
ORD
- DRO
1 stop8h 02m
American Airlines
Deal found 3/17![American Airlines logo]()
$328
This Delta deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 8/610:57 am
COS
- ORD
1 stop7h 46m
Delta
Mon 8/106:00 am
ORD
- COS
1 stop5h 02m
Delta
Deal found 3/14![Delta logo]()
$309
This United Airlines deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/211:43 am
COS
- ORD
Nonstop2h 44m
United Airlines
Tue 5/58:46 am
ORD
- COS
Nonstop3h 01m
United Airlines
Deal found 3/17![United Airlines logo]()
$281
This Southwest deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 5/295:35 pm
DEN
- MDW
Nonstop2h 30m
Southwest
Mon 6/16:00 am
MDW
- DEN
Nonstop2h 40m
Southwest
Deal found 3/14![Southwest logo]()
$233
This United Airlines deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/165:45 pm
DEN
- STL
Nonstop2h 09m
United Airlines
Tue 4/218:54 am
STL
- DEN
Nonstop2h 33m
United Airlines
Deal found 3/18![United Airlines logo]()
$281
This Southwest deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/168:20 pm
DEN
- MDW
Nonstop2h 20m
Southwest
Sun 4/196:00 am
MDW
- DEN
Nonstop2h 40m
Southwest
Deal found 3/17![Southwest logo]()
$233
Last-minute flights from Colorado to IllinoisDiscover last-minute flight deals from Colorado to Illinois. Data last updated March 19, 2026 and is based on user searches.
Discover last-minute flight deals from Colorado to Illinois. Data last updated March 19, 2026 and is based on user searches.
This Cheapflightsfares deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 3/279:19 pm
DEN
- ORD
Nonstop2h 38m
Frontier
Wed 4/13:29 pm
ORD
- DEN
Nonstop3h 08m
Frontier
Deal found 3/16![Frontier logo]()
$174
This Kiwi.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/16:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 4/68:19 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/18![Frontier logo]()
$107
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/16:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$127
This Cheapflightsfares deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 4/66:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/15![Frontier logo]()
$105
This Frontier deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Sat 4/118:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/14![Frontier logo]()
$106
This Frontier deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Wed 4/88:16 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/14![Frontier logo]()
$112
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 4/106:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Mon 4/138:19 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$121
This Super.com deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 4/136:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Sat 4/184:16 pm
STL
- DEN
1 stop9h 03m
Frontier
Deal found 3/17![Frontier logo]()
$134
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/164:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Thu 4/238:06 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$131
This Priceline deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 4/264:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Mon 4/278:17 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$118
This Cheapflightsfares deal was found by Cheapflights users on 3/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 4/274:20 pm
DEN
- STL
Nonstop2h 12m
Frontier
Thu 4/308:06 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/15![Frontier logo]()
$135
This Kiwi.com deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/304:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Mon 5/48:17 pm
STL
- DEN
Nonstop2h 33m
Frontier
Deal found 3/17![Frontier logo]()
$111
One-way flights from Colorado to IllinoisSearch for one-way flight options from Colorado to Illinois. Find affordable one-way fares based on user searches. Data last updated March 19, 2026.
Search for one-way flight options from Colorado to Illinois. Find affordable one-way fares based on user searches. Data last updated March 19, 2026.
This Kiwi.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 4/36:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Deal found 3/18![Frontier logo]()
$43
This Super.com deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 4/174:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Deal found 3/17![Frontier logo]()
$44
This Kiwi.com deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 4/46:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Deal found 3/16![Frontier logo]()
$49
This Frontier deal was found by Cheapflights users on 3/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 4/136:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Deal found 3/14![Frontier logo]()
$50
This Kiwi.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/304:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Deal found 3/18![Frontier logo]()
$55
This Priceline deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 4/164:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Deal found 3/17![Frontier logo]()
$56
This Super.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 5/14:09 pm
DEN
- STL
Nonstop2h 12m
Frontier
Deal found 3/18![Frontier logo]()
$63
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 4/86:40 am
DEN
- STL
Nonstop2h 08m
Frontier
Deal found 3/17![Frontier logo]()
$64
This Super.com deal was found by Cheapflights users on 3/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 5/174:15 pm
DEN
- STL
Nonstop2h 08m
Frontier
Deal found 3/18![Frontier logo]()
$73
This Cheapflightsfares deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 5/1111:54 pm
DEN
- ORD
1 stop7h 01m
Frontier
Deal found 3/17![Frontier logo]()
$90
This Priceline deal was found by Cheapflights users on 3/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 6/65:05 am
DEN
- MDW
1 stop8h 07m
Frontier
Deal found 3/17![Frontier logo]()
$90
This Cheapflightsfares deal was found by Cheapflights users on 3/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 4/119:00 pm
DEN
- ORD
Nonstop2h 38m
Frontier
Deal found 3/16![Frontier logo]()
$91
Find flight deals from Colorado to Illinois
Keep the following information in mind while searching for Colorado to Illinois flight deals. Data was last updated March 19, 2026.
Most accurate provider | FlightHub 3 stars |
|---|---|
Most trusted provider | FlightHub 3 stars |
Round-trip from | $105 (Cheapflightsfares) |
One-way from | $43 (Kiwi.com) |
Popular in | March |
Cheapest in | August |
Average price | $275 |
Good round-trip deal | $248 or less |
Good one-way deal | $158 or less |
Cheapflights Fare Finder
Customize your flight search to find flights from Colorado to Illinois that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated March 19, 2026.
Use the filters below to find and compare flights from Colorado to Illinois that are best for you.
Fly from
Fly to
Route
Depart
Return
Cheapest round-trip
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Sat 4/18
6:30 am-9:50 am
Nonstop2h 20m
Chicago Midway
Sat 4/18
5:30 pm-7:10 pm
Nonstop2h 40m
$215
DenverChicago
DEN - ORD
DENORD
Denver Intl
Sat 4/18
10:50 am-2:20 pm
Nonstop2h 30m
Chicago O'Hare Intl
Mon 4/20
6:15 pm-8:05 pm
Nonstop2h 50m
$218
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Wed 5/27
6:35 am-9:55 am
Nonstop2h 20m
Chicago Midway
Sat 5/30
10:30 am-2:15 pm
1 stop4h 45m
$218
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Thu 4/30
8:20 pm-11:40 pm
Nonstop2h 20m
Chicago Midway
Thu 5/7
9:35 pm-11:15 pm
Nonstop2h 40m
$221
DenverChicago
DEN - ORD
DENORD
Denver Intl
Tue 4/21
4:35 pm-8:14 pm
Nonstop2h 39m
Chicago O'Hare Intl
Sun 4/26
11:03 pm-12:58 am
Nonstop2h 55m
$223
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Wed 6/3
6:35 am-9:55 am
Nonstop2h 20m
Chicago Midway
Fri 6/12
5:15 am-6:50 am
Nonstop2h 35m
$223
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Sat 5/9
11:40 am-5:15 pm
1 stop4h 35m
Chicago Midway
Mon 5/11
9:35 pm-11:15 pm
Nonstop2h 40m
$224
Colorado SpringsSt. Louis
COS - STL
COSSTL
Colorado Springs
Wed 4/15
1:14 pm-9:19 pm
1 stop7h 05m
Lambert-St Louis
Tue 4/21
9:59 am-10:13 pm
2 stops13h 14m
$226
DenverChicago
DEN - ORD
DENORD
Denver Intl
Tue 4/7
6:15 am-12:50 pm
1 stop5h 35m
Chicago O'Hare Intl
Wed 4/8
11:55 am-7:25 pm
2 stops8h 30m
$226
DenverChicago
DEN - MDW
DENMDW
Denver Intl
Thu 4/9
6:35 am-9:55 am
Nonstop2h 20m
Chicago Midway
Thu 4/9
3:35 pm-8:00 pm
1 stop5h 25m
$231
Showing 1-10 of 60 resultsSorted by cheapest first
Best time to book a flight from Colorado to Illinois
Have a flexible travel schedule? Discover the best time to fly to Illinois from Colorado with our price prediction graph.
DEN-STL
DEN-ORD
DEN-MDW
COS-STL
COS-MDW
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.
Cheapflights Insights
Everything you need to know about your flight from Colorado to Illinois
USCO-USIL
DEN-STL
DEN-ORD
DEN-MDW
COS-STL
What is the cheapest month to book a flight from Colorado to Illinois?
Currently, July is the cheapest month in which you can book a flight from Colorado to Illinois (average of $46). Flying from Colorado to Illinois in June is currently the most expensive (average of $140). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.
What is the cheapest time of day to fly from CO to IL?
Find hourly flight availability from Colorado to Illinois. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated March 19, 2026.
A simple way to save on the total cost of your ticket is to fly from Colorado to Illinois in the evening. If you’re flexible enough to do this you can expect to save up to 41% on your trip compared to booking a flight at noon.
What is the cheapest day to fly from Colorado to Illinois?
Use this chart to determine the cheapest time to fly round-trip from Colorado to Illinois. Price data was last updated on March 14, 2026.
Travelers seeking maximum savings on their Colorado to Illinois flight should consider departing on Friday at noon when fares are most often at their lowest. Sunday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.
Weekly flight availability from Colorado to Illinois
Explore weekly flight availability from Colorado to Illinois. Discover flights operating on different days of the week, giving you the flexibility to choose a travel day that best fits your plans. Compare info to find the most convenient option for your journey. Data last updated March 19, 2026.
The most flights from USCO to USIL are scheduled on a Wednesday (55 on average). You will have fewer flight options on Saturday, which is when the least amount of flights are scheduled (40 on average).
Reviews of airlines servicing Illinois
Get insights into the airlines that provide service to Illinois. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to Illinois. Reviews last updated March 19, 2026.
Read reviews from past customers who have flown Southwest,United Airlines, andAllegiant Air from Colorado to Illinois. You can also see how each airline compares in terms of entertainment options, comfort, food, crew/service, and boarding process.
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Crew
8.6
Comfort
8.0
Entertainment
7.5
Boarding
8.1
Food
7.0
Overall
8.0
Reviews
1 / 20
10.0
ExcellentAnonymous,Mar 2026
KOA - HNL
Related info for your journey
Find useful and relevant information for your journey from Colorado to Illinois. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.
Browse thousands of different options on Cheapflights for your next trip
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Alternative routes for Colorado to Illinois
See prices for flight routes from nearby airports that may be better suited for you.
Complete your trip
Complete your trip to Illinois by adding a car rental and/or hotel reservation to your travel itinerary.
Search flights from Colorado to Illinois by cabin class
Find flights from Colorado to Illinois, based on your preferred cabin class, be it economy, premium economy, business, or first class.
Colorado and Illinois flights
Browse other Colorado and Illinois flight options. Last updated on March 19, 2026.
Popular flight searches
Check out other popular destinations found by fellow travelers in 2026
Find a return flight route from Illinois
Find the right flight back to Colorado after your stay in Illinois
Colorado to Illinois flights
Consider these flights traveling from Colorado to Illinois.
Top 6 airlines flying from Colorado to Illinois
Discover the top 6 airlines that operate flights from Colorado to Illinois. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated March 19, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$57 | Average$140 | FlexibilityNo cancel fee | On-time88% | |
| Cheapest$74 | Average$185 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$126 | Average$191 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$155 | Average$292 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$157 | Average$431 | FlexibilityNo cancel fee | On-time71% | |
| Cheapest$161 | Average$425 | FlexibilityNo cancel fee | On-time69% |