$76+ Cheap flights from Ontario (ONT) 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 9/1. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Jun 18 — Jun 251
Round-trip
1 adult, Economy
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Find cheap flights from Ontario to Illinois with Cheapflights
1. Tell us where you want to go
Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”2. Select your favorite providers
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Cheapest flights from Ontario to IllinoisExplore the most affordable flight options available from Ontario to Illinois. Find the lowest fares from popular airlines and budget airlines, with prices last updated on May 19, 2026.
Explore the most affordable flight options available from Ontario to Illinois. Find the lowest fares from popular airlines and budget airlines, with prices last updated on May 19, 2026.
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/126:00 am
ONT
- STL
1 stop11h 23m
Frontier
Wed 8/268:08 pm
STL
- ONT
1 stop15h 57m
Frontier
Deal found 5/14![Frontier logo]()
$197
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/1210:49 am
ONT
- STL
1 stop6h 34m
Frontier
Mon 8/315:33 pm
STL
- ONT
2 stops32h 16m
Frontier
Deal found 5/14![Frontier logo]()
$200
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/1210:49 am
ONT
- STL
1 stop6h 34m
Frontier
Fri 8/285:33 pm
STL
- ONT
2 stops26h 19m
Frontier
Deal found 5/14![Frontier logo]()
$216
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/1210:49 am
ONT
- STL
1 stop6h 34m
Frontier
Tue 9/13:33 pm
STL
- ONT
2 stops10h 16m
Frontier
Deal found 5/14![Frontier logo]()
$224
This Trip.com deal was found by Cheapflights users on 5/17. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/126:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sat 8/158:08 pm
STL
- ONT
1 stop5h 42m
Frontier
Deal found 5/17![Frontier logo]()
$230
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 8/1810:50 am
ONT
- STL
2 stops20h 02m
Frontier
Tue 9/18:08 pm
STL
- ONT
1 stop15h 57m
Frontier
Deal found 5/14![Frontier logo]()
$239
This Trip.com deal was found by Cheapflights users on 5/14. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/156:00 am
ONT
- STL
1 stop11h 23m
Frontier
Mon 7/202:52 pm
STL
- ONT
1 stop7h 01m
Frontier
Deal found 5/14![Frontier logo]()
$259
This Trip.com deal was found by Cheapflights users on 5/14. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/156:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sun 7/192:52 pm
STL
- ONT
1 stop7h 01m
Frontier
Deal found 5/14![Frontier logo]()
$260
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/1210:49 am
ONT
- STL
1 stop6h 34m
Frontier
Sun 8/308:21 pm
STL
- ONT
1 stop20h 48m
Frontier
Deal found 5/14![Frontier logo]()
$261
This Southwest deal was found by Cheapflights users on 5/16. 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 9/91:50 pm
ONT
- MDW
1 stop7h 00m
Southwest
Sat 9/194:05 pm
MDW
- ONT
1 stop6h 00m
Southwest
Deal found 5/16![Southwest logo]()
$273
This Delta deal was found by Cheapflights users on 5/18. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/2211:55 am
ONT
- ORD
1 stop9h 52m
Delta
Mon 9/286:59 pm
ORD
- ONT
1 stop6h 45m
Delta
Deal found 5/18![Delta logo]()
$273
This Delta deal was found by Cheapflights users on 5/18. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/2212:00 pm
ONT
- MDW
1 stop7h 46m
Delta
Mon 9/289:30 am
MDW
- ONT
2 stops8h 44m
Delta
Deal found 5/18![Delta logo]()
$278
Best flights from Ontario to IllinoisDiscover carefully curated flight deals from Ontario to Illinois that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated May 19, 2026.
Discover carefully curated flight deals from Ontario to Illinois that have cost, travel time, and layovers in mind to ensure you get the best travel experience. Data last updated May 19, 2026.
This Southwest deal was found by Cheapflights users on 5/16. 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 9/91:50 pm
ONT
- MDW
1 stop7h 00m
Southwest
Sat 9/194:05 pm
MDW
- ONT
1 stop6h 00m
Southwest
Deal found 5/16![Southwest logo]()
$273
This Delta deal was found by Cheapflights users on 5/15. 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 9/2210:59 pm
ONT
- MDW
2 stops11h 31m
Delta
Mon 9/286:00 am
MDW
- ONT
2 stops12h 14m
Delta
Deal found 5/15![Delta logo]()
$293
This Alaska Airlines deal was found by Cheapflights users on 5/15. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 10/266:54 pm
ONT
- ORD
1 stop9h 26m
Alaska Airlines
Wed 10/289:00 am
ORD
- ONT
1 stop11h 00m
Alaska Airlines
Deal found 5/15![Alaska Airlines logo]()
$307
This Frontier deal was found by Cheapflights users on 5/13. 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.
Sat 7/116:00 am
ONT
- STL
1 stop11h 23m
Frontier
Mon 8/248:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 5/13![Frontier logo]()
$310
This United Airlines deal was found by Cheapflights users on 5/17. 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.
Tue 6/166:05 am
ONT
- ORD
Nonstop4h 15m
United Airlines
Tue 6/308:18 pm
ORD
- ONT
Nonstop4h 33m
United Airlines
Deal found 5/17![United Airlines logo]()
$389
This American Airlines deal was found by Cheapflights users on 5/16. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 6/611:59 pm
ONT
- MLI
1 stop8h 40m
American Airlines
Sat 6/134:42 pm
MLI
- ONT
1 stop9h 17m
American Airlines
Deal found 5/16![American Airlines logo]()
$392
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 6/123:34 pm
ONT
- RFD
2 stops18h 40m
Multiple Airlines
Sun 6/141:13 pm
RFD
- ONT
1 stop8h 38m
Multiple Airlines
Deal found 5/14![Multiple Airlines logo]()
$518
This Delta deal was found by Cheapflights users on 5/16. 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 8/1310:00 pm
ONT
- MDW
2 stops12h 39m
Delta
Mon 8/171:27 pm
MDW
- ONT
2 stops12h 07m
Delta
Deal found 5/16![Delta logo]()
$317
This CheapOair deal was found by Cheapflights users on 5/17. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 6/253:34 pm
ONT
- STL
1 stop20h 32m
Frontier
Sun 6/282:56 pm
STL
- ONT
1 stop26h 12m
Frontier
Deal found 5/17![Frontier logo]()
$319
This Southwest deal was found by Cheapflights users on 5/15. 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.
Tue 7/281:30 pm
ONT
- MDW
1 stop7h 35m
Southwest
Thu 8/68:00 am
MDW
- ONT
2 stops9h 05m
Southwest
Deal found 5/15![Southwest logo]()
$333
This Frontier deal was found by Cheapflights users on 5/13. 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.
Sun 7/126:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sun 8/238:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 5/13![Frontier logo]()
$330
This Southwest deal was found by Cheapflights users on 5/17. 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.
Sun 7/1211:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Wed 7/1512:20 pm
MDW
- ONT
2 stops6h 45m
Southwest
Deal found 5/17![Southwest logo]()
$343
This Delta deal was found by Cheapflights users on 5/14. 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.
Tue 9/2212:00 pm
ONT
- MDW
1 stop7h 46m
Delta
Fri 9/2510:35 am
MDW
- ONT
1 stop9h 26m
Delta
Deal found 5/14![Delta logo]()
$347
This United Airlines deal was found by Cheapflights users on 5/18. 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 8/257:00 am
ONT
- ORD
Nonstop4h 10m
United Airlines
Sun 8/305:30 pm
ORD
- ONT
Nonstop4h 27m
United Airlines
Deal found 5/18![United Airlines logo]()
$428
This Southwest deal was found by Cheapflights users on 5/18. 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 Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 8/155:40 am
ONT
- MDW
2 stops8h 20m
Southwest
Tue 8/1810:30 am
MDW
- ONT
2 stops7h 35m
Southwest
Deal found 5/18![Southwest logo]()
$368
This Frontier deal was found by Cheapflights users on 5/15. 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.
Sat 6/136:00 am
ONT
- STL
1 stop10h 53m
Frontier
Wed 6/178:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 5/15![Frontier logo]()
$374
This American Airlines deal was found by Cheapflights users on 5/15. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/305:44 am
ONT
- PIA
1 stop8h 13m
American Airlines
Tue 6/24:20 pm
PIA
- ONT
1 stop8h 16m
American Airlines
Deal found 5/15![American Airlines logo]()
$464
This Delta deal was found by Cheapflights users on 5/16. 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.
Sun 8/1610:00 pm
ONT
- MDW
2 stops12h 39m
Delta
Sat 8/226:05 am
MDW
- ONT
2 stops12h 19m
Delta
Deal found 5/16![Delta logo]()
$392
This United Airlines deal was found by Cheapflights users on 5/13. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 7/246:10 am
ONT
- ORD
Nonstop4h 15m
United Airlines
Wed 7/298:18 pm
ORD
- ONT
Nonstop4h 33m
United Airlines
Deal found 5/13![United Airlines logo]()
$448
This Southwest deal was found by Cheapflights users on 5/16. 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.
Sun 8/1611:55 pm
ONT
- MDW
Nonstop3h 50m
Southwest
Sat 8/226:50 am
MDW
- ONT
1 stop5h 30m
Southwest
Deal found 5/16![Southwest logo]()
$372
This American Airlines deal was found by Cheapflights users on 5/17. 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.
Tue 6/167:13 pm
ONT
- PIA
2 stops12h 10m
American Airlines
Tue 6/2312:24 pm
PIA
- ONT
2 stops11h 33m
American Airlines
Deal found 5/17![American Airlines logo]()
$493
This United Airlines deal was found by Cheapflights users on 5/18. 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.
Sat 11/147:00 am
ONT
- BMI
1 stop8h 52m
United Airlines
Tue 11/179:44 am
BMI
- ONT
2 stops12h 36m
United Airlines
Deal found 5/18![United Airlines logo]()
$454
This Kiwi.com deal was found by Cheapflights users on 5/18. 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 5/298:03 am
ONT
- RFD
2 stops23h 18m
Multiple Airlines
Sun 5/311:11 pm
RFD
- ONT
1 stop27h 58m
Multiple Airlines
Deal found 5/18![Multiple Airlines logo]()
$588
This Delta deal was found by Cheapflights users on 5/14. 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 7/3011:48 am
ONT
- MLI
1 stop8h 43m
Delta
Sat 8/1511:08 am
MLI
- ONT
1 stop9h 21m
Delta
Deal found 5/14![Delta logo]()
$449
This American Airlines deal was found by Cheapflights users on 5/16. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/512:33 pm
ONT
- PIA
1 stop8h 46m
American Airlines
Sun 8/97:12 am
PIA
- ONT
1 stop8h 19m
American Airlines
Deal found 5/16![American Airlines logo]()
$494
This United Airlines deal was found by Cheapflights users on 5/13. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 7/161:18 pm
ONT
- STL
1 stop5h 25m
United Airlines
Wed 7/221:13 pm
STL
- ONT
2 stops11h 24m
United Airlines
Deal found 5/13![United Airlines logo]()
$463
This Delta deal was found by Cheapflights users on 5/14. 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.
Tue 8/412:32 pm
ONT
- MLI
1 stop7h 56m
Delta
Sat 8/1511:08 am
MLI
- ONT
1 stop9h 21m
Delta
Deal found 5/14![Delta logo]()
$449
This Alaska Airlines deal was found by Cheapflights users on 5/17. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/125:54 pm
ONT
- MLI
2 stops15h 15m
Alaska Airlines
Wed 8/1911:39 am
MLI
- ONT
2 stops13h 45m
Alaska Airlines
Deal found 5/17![Alaska Airlines logo]()
$673
This Southwest deal was found by Cheapflights users on 5/18. 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 Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 7/24:20 pm
ONT
- MDW
1 stop6h 40m
Southwest
Thu 7/95:15 am
MDW
- ONT
2 stops8h 05m
Southwest
Deal found 5/18![Southwest logo]()
$462
This United Airlines deal was found by Cheapflights users on 5/17. 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 8/15:45 am
ONT
- ORD
1 stop9h 44m
United Airlines
Mon 8/108:18 pm
ORD
- ONT
Nonstop4h 33m
United Airlines
Deal found 5/17![United Airlines logo]()
$472
Last-minute flights from Ontario to IllinoisDiscover last-minute flight deals from Ontario to Illinois. Data last updated May 19, 2026 and is based on user searches.
Discover last-minute flight deals from Ontario to Illinois. Data last updated May 19, 2026 and is based on user searches.
This Frontier deal was found by Cheapflights users on 5/13. 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.
Tue 6/26:00 am
ONT
- STL
1 stop11h 23m
Frontier
Wed 6/38:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 5/13![Frontier logo]()
$285
This Kiwi.com deal was found by Cheapflights users on 5/13. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 6/28:06 pm
ONT
- ORD
2 stops21h 23m
Frontier
Tue 6/99:48 pm
ORD
- ONT
1 stop14h 17m
Frontier
Deal found 5/13![Frontier logo]()
$287
This Gotogate deal was found by Cheapflights users on 5/13. 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 Gotogate is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/310:50 am
ONT
- ORD
1 stop7h 42m
Frontier
Tue 6/95:29 pm
ORD
- ONT
1 stop26h 23m
Frontier
Deal found 5/13![Frontier logo]()
$279
This Frontier deal was found by Cheapflights users on 5/13. 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.
Thu 6/410:50 am
ONT
- STL
1 stop6h 33m
Frontier
Fri 6/127:38 pm
STL
- ONT
1 stop6h 11m
Frontier
Deal found 5/13![Frontier logo]()
$290
This Frontier deal was found by Cheapflights users on 5/13. 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.
Sat 6/66:00 am
ONT
- ORD
1 stop12h 32m
Frontier
Wed 6/107:20 am
ORD
- ONT
1 stop9h 48m
Frontier
Deal found 5/13![Frontier logo]()
$280
This Expedia deal was found by Cheapflights users on 5/17. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/103:34 pm
ONT
- STL
1 stop20h 32m
Frontier
Tue 6/167:46 pm
STL
- ONT
1 stop21h 22m
Frontier
Deal found 5/17![Frontier logo]()
$270
This Expedia deal was found by Cheapflights users on 5/16. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/101:33 pm
ONT
- STL
1 stop22h 33m
Frontier
Mon 6/152:56 pm
STL
- ONT
1 stop20h 11m
Frontier
Deal found 5/16![Frontier logo]()
$289
This CheapOair deal was found by Cheapflights users on 5/18. 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.
Tue 6/166:00 am
ONT
- ORD
1 stop12h 43m
Frontier
Thu 6/189:48 pm
ORD
- ONT
1 stop14h 17m
Frontier
Deal found 5/18![Frontier logo]()
$289
This Expedia deal was found by Cheapflights users on 5/18. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/243:34 pm
ONT
- ORD
1 stop11h 33m
Frontier
Fri 6/269:48 pm
ORD
- ONT
1 stop14h 17m
Frontier
Deal found 5/18![Frontier logo]()
$290
This Expedia deal was found by Cheapflights users on 5/14. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 6/275:43 pm
ONT
- ORD
1 stop29h 05m
Frontier
Tue 7/75:46 pm
ORD
- ONT
1 stop26h 03m
Frontier
Deal found 5/14![Frontier logo]()
$284
This Mytrip deal was found by Cheapflights users on 5/16. 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 Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 6/303:34 pm
ONT
- STL
1 stop25h 17m
Frontier
Tue 7/78:08 pm
STL
- ONT
1 stop15h 55m
Frontier
Deal found 5/16![Frontier logo]()
$279
This Expedia deal was found by Cheapflights users on 5/17. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 6/301:33 pm
ONT
- STL
1 stop27h 18m
Frontier
Sat 7/188:08 pm
STL
- ONT
1 stop5h 42m
Frontier
Deal found 5/17![Frontier logo]()
$284
One-way flights from Ontario to IllinoisSearch for one-way flight options from Ontario to Illinois. Find affordable one-way fares based on user searches. Data last updated May 19, 2026.
Search for one-way flight options from Ontario to Illinois. Find affordable one-way fares based on user searches. Data last updated May 19, 2026.
This Trip.com deal was found by Cheapflights users on 5/18. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/16:00 am
ONT
- ORD
1 stop12h 53m
Frontier
Deal found 5/18![Frontier logo]()
$76
This Trip.com deal was found by Cheapflights users on 5/15. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/126:00 am
ONT
- ORD
1 stop12h 52m
Frontier
Deal found 5/15![Frontier logo]()
$80
This Kiwi.com deal was found by Cheapflights users on 5/15. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 7/213:40 pm
ONT
- ORD
1 stop11h 48m
Frontier
Deal found 5/15![Frontier logo]()
$104
This Trip.com deal was found by Cheapflights users on 5/19. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 7/73:40 pm
ONT
- ORD
1 stop11h 48m
Frontier
Deal found 5/19![Frontier logo]()
$107
This Kiwi.com deal was found by Cheapflights users on 5/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/1711:38 am
ONT
- ORD
1 stop20h 23m
Frontier
Deal found 5/14![Frontier logo]()
$109
This Southwest deal was found by Cheapflights users on 5/17. 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 8/1111:55 pm
ONT
- MDW
Nonstop3h 50m
Southwest
Deal found 5/17![Southwest logo]()
$110
This United Airlines deal was found by Cheapflights users on 5/15. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 7/71:50 pm
ONT
- ORD
1 stop9h 09m
United Airlines
Deal found 5/15![United Airlines logo]()
$115
This Delta deal was found by Cheapflights users on 5/14. 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 7/1511:48 am
ONT
- MDW
1 stop8h 27m
Delta
Deal found 5/14![Delta logo]()
$119
This Delta deal was found by Cheapflights users on 5/14. 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.
Tue 7/211:00 pm
ONT
- ORD
1 stop6h 48m
Delta
Deal found 5/14![Delta logo]()
$119
This Delta deal was found by Cheapflights users on 5/18. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 11/1010:59 pm
ONT
- MDW
1 stop8h 53m
Delta
Deal found 5/18![Delta logo]()
$120
This Delta deal was found by Cheapflights users on 5/18. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 6/1011:57 am
ONT
- ORD
1 stop9h 42m
Delta
Deal found 5/18![Delta logo]()
$120
This Delta deal was found by Cheapflights users on 5/14. 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.
Tue 7/76:00 am
ONT
- MDW
2 stops10h 18m
Delta
Deal found 5/14![Delta logo]()
$124
Find flight deals from Ontario to Illinois
Keep the following information in mind while searching for Ontario to Illinois flight deals. Data was last updated May 19, 2026.
Most accurate provider | FlightHub 3 stars |
|---|---|
Most trusted provider | FlightHub 3 stars |
Round-trip from | $197 (Kiwi.com) |
One-way from | $76 (Trip.com) |
Popular in | February |
Cheapest in | September |
Average price | $337 |
Good round-trip deal | $412 or less |
Good one-way deal | $228 or less |
Cheapflights Fare Finder
Customize your flight search to find flights from Ontario 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 May 19, 2026.
Use the filters below to find and compare flights from Ontario to Illinois that are best for you.
Fly from
Fly to
Route
Depart
Return
Cheapest round-trip
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Wed 9/9
1:50 pm-10:50 pm
1 stop7h 00m
Chicago Midway
Sat 9/19
4:05 pm-8:05 pm
1 stop6h 00m
$273
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Tue 9/22
10:59 pm-12:30 pm
2 stops11h 31m
Chicago Midway
Mon 9/28
6:00 am-4:14 pm
2 stops12h 14m
$293
OntarioChicago
ONT - ORD
ONTORD
Ontario
Mon 10/26
6:54 pm-6:20 am
1 stop9h 26m
Chicago O'Hare Intl
Wed 10/28
9:00 am-6:00 pm
1 stop11h 00m
$307
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 7/11
6:00 am-7:23 pm
1 stop11h 23m
Lambert-St Louis
Mon 8/24
8:08 pm-11:49 pm
1 stop5h 41m
$310
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Thu 8/13
10:00 pm-12:39 pm
2 stops12h 39m
Chicago Midway
Mon 8/17
1:27 pm-11:34 pm
2 stops12h 07m
$317
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 6/25
3:34 pm-2:06 pm
1 stop20h 32m
Lambert-St Louis
Sun 6/28
2:56 pm-3:08 pm
1 stop26h 12m
$319
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sun 7/12
6:00 am-7:23 pm
1 stop11h 23m
Lambert-St Louis
Sun 8/23
8:08 pm-11:49 pm
1 stop5h 41m
$330
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Tue 7/28
1:30 pm-11:05 pm
1 stop7h 35m
Chicago Midway
Thu 8/6
8:00 am-3:05 pm
2 stops9h 05m
$333
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Sun 7/12
11:55 pm-5:40 am
Nonstop3h 45m
Chicago Midway
Wed 7/15
12:20 pm-5:05 pm
2 stops6h 45m
$343
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Tue 9/22
12:00 pm-9:46 pm
1 stop7h 46m
Chicago Midway
Fri 9/25
10:35 am-6:01 pm
1 stop9h 26m
$347
Showing 1-10 of 60 resultsSorted by cheapest first
Best time to book a flight from Ontario to Illinois
Have a flexible travel schedule? Discover the best time to fly to Illinois from Ontario with our price prediction graph.
ONT-STL
ONT-ORD
ONT-MDW
ONT-RFD
ONT-MLI
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 Ontario to Illinois
ONT-USIL
ONT-STL
ONT-ORD
ONT-MDW
ONT-RFD
How far ahead should I book a flight from Ontario to Illinois?
The best time to book flights from Ontario to Illinois is 73 days before your desired departure date. The cost of your flight will likely increase significantly if you book two weeks in advance of your flight.
What is the cheapest month to book a flight from Ontario to Illinois?
Currently, September is the cheapest month in which you can book a flight from Ontario to Illinois (average of $102). Flying from Ontario to Illinois in March is currently the most expensive (average of $186). 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 ONT to IL?
Find hourly flight availability from Ontario 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 May 19, 2026.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Ontario to Illinois as you normally would.
How much does it cost to fly round-trip from Ontario to Illinois?
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 May 19, 2026.
Read through reviews of airlines operating flights from Ontario to Illinois, such as Southwest,Delta, andUnited Airlines. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Comfort
8.0
Crew
8.6
Food
7.0
Overall
7.9
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Related info for your journey
Find useful and relevant information for your journey from Ontario to Illinois. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.
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Alternative routes for Ontario 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 Ontario to Illinois by cabin class
Find flights from Ontario to Illinois, based on your preferred cabin class, be it economy, premium economy, business, or first class.
Ontario and Illinois flights
Browse other Ontario and Illinois flight options. Last updated on May 19, 2026.
Popular flight searches
Check out other popular destinations found by fellow travelers in 2026
Ontario to Illinois flights
Consider these flights traveling from Ontario to Illinois.
Top 5 airlines flying from Ontario to Illinois
Discover the top 5 airlines that operate flights from Ontario 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 May 19, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$117 | Average$258 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$226 | Average$458 | FlexibilityNo cancel fee | On-time69% | |
| Cheapest$258 | Average$428 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$260 | Average$446 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$288 | Average$472 | FlexibilityNo cancel fee | On-time71% |