$60+ 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 5/6. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
May 13 — May 201
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 April 13, 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 April 13, 2026.
This Frontier deal was found by Cheapflights users on 4/8. 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 5/88:44 am
ONT
- STL
1 stop9h 39m
Frontier
Thu 5/1412:36 pm
STL
- ONT
1 stop8h 56m
Frontier
Deal found 4/8![Frontier logo]()
$160
This Frontier deal was found by Cheapflights users on 4/11. 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 5/48:59 pm
ONT
- STL
1 stop19h 07m
Frontier
Sun 5/1012:36 pm
STL
- ONT
1 stop21h 13m
Frontier
Deal found 4/11![Frontier logo]()
$162
This Booking.com deal was found by Cheapflights users on 4/8. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/238:43 am
ONT
- STL
1 stop8h 48m
Frontier
Mon 5/259:06 pm
STL
- ONT
1 stop12h 58m
Frontier
Deal found 4/8![Frontier logo]()
$167
This Kiwi.com deal was found by Cheapflights users on 4/9. 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 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Sun 5/1012:36 pm
STL
- ONT
1 stop21h 13m
Frontier
Deal found 4/9![Frontier logo]()
$168
This CheapOair deal was found by Cheapflights users on 4/8. 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.
Wed 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Fri 5/159:18 pm
STL
- ONT
1 stop19h 51m
Frontier
Deal found 4/8![Frontier logo]()
$171
This Booking.com deal was found by Cheapflights users on 4/10. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 5/1111:36 am
ONT
- STL
1 stop28h 30m
Frontier
Tue 5/196:51 pm
STL
- ONT
1 stop22h 53m
Frontier
Deal found 4/10![Frontier logo]()
$172
This Trip.com deal was found by Cheapflights users on 4/12. 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 5/276:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sun 6/78:08 pm
STL
- ONT
1 stop15h 57m
Frontier
Deal found 4/12![Frontier logo]()
$174
This Kiwi.com deal was found by Cheapflights users on 4/11. 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 5/15:33 pm
ONT
- STL
1 stop23h 59m
Frontier
Tue 5/56:51 pm
STL
- ONT
1 stop22h 53m
Frontier
Deal found 4/11![Frontier logo]()
$175
This Kiwi.com deal was found by Cheapflights users on 4/8. 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 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Wed 5/66:51 pm
STL
- ONT
2 stops17h 14m
Frontier
Deal found 4/8![Frontier logo]()
$177
This Gotogate deal was found by Cheapflights users on 4/10. 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.
Thu 4/305:43 pm
ONT
- STL
1 stop23h 38m
Frontier
Mon 5/49:55 pm
STL
- ONT
1 stop19h 49m
Frontier
Deal found 4/10![Frontier logo]()
$180
This Frontier deal was found by Cheapflights users on 4/10. 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 5/238:43 am
ONT
- STL
1 stop8h 48m
Frontier
Sat 6/68:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 4/10![Frontier logo]()
$185
This Delta deal was found by Cheapflights users on 4/12. 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.
Sat 5/212:49 pm
ONT
- MDW
1 stop7h 39m
Delta
Tue 5/51:24 pm
MDW
- ONT
2 stops9h 36m
Delta
Deal found 4/12![Delta logo]()
$254
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 April 13, 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 April 13, 2026.
This CheapOair deal was found by Cheapflights users on 4/7. 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 6/1811:43 am
ONT
- STL
1 stop5h 53m
Frontier
Sun 6/218:21 pm
STL
- ONT
1 stop25h 27m
Frontier
Deal found 4/7![Frontier logo]()
$261
This Delta deal was found by Cheapflights users on 4/8. 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 5/285:50 pm
ONT
- MDW
2 stops12h 52m
Delta
Thu 6/41:22 pm
MDW
- ONT
2 stops12h 12m
Delta
Deal found 4/8![Delta logo]()
$292
This United Airlines deal was found by Cheapflights users on 4/12. 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 5/77:00 am
ONT
- ORD
Nonstop4h 03m
United Airlines
Wed 5/138:09 pm
ORD
- ONT
Nonstop4h 26m
United Airlines
Deal found 4/12![United Airlines logo]()
$296
This Southwest deal was found by Cheapflights users on 4/8. 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 5/111:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Tue 5/52:55 pm
MDW
- ONT
1 stop8h 50m
Southwest
Deal found 4/8![Southwest logo]()
$324
This Kiwi.com deal was found by Cheapflights users on 4/12. 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 4/297:44 pm
ONT
- RFD
1 stop14h 16m
Multiple Airlines
Sun 5/312:50 pm
RFD
- ONT
1 stop21h 14m
Multiple Airlines
Deal found 4/12![Multiple Airlines logo]()
$324
This American Airlines deal was found by Cheapflights users on 4/13. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 4/282:08 pm
ONT
- MLI
1 stop7h 21m
American Airlines
Sat 5/212:51 pm
MLI
- ONT
2 stops8h 43m
American Airlines
Deal found 4/13![American Airlines logo]()
$424
This Alaska Airlines deal was found by Cheapflights users on 4/11. 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.
Tue 5/56:00 am
ONT
- STL
1 stop7h 50m
Alaska Airlines
Sat 5/97:00 am
STL
- ONT
1 stop9h 32m
Alaska Airlines
Deal found 4/11![Alaska Airlines logo]()
$439
This CheapOair deal was found by Cheapflights users on 4/7. 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.
Wed 6/246:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sun 6/288:21 pm
STL
- ONT
1 stop25h 27m
Frontier
Deal found 4/7![Frontier logo]()
$281
This CheapOair deal was found by Cheapflights users on 4/7. 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 stop26h 02m
Frontier
Mon 6/298:21 pm
STL
- ONT
1 stop20h 48m
Frontier
Deal found 4/7![Frontier logo]()
$301
This Southwest deal was found by Cheapflights users on 4/9. 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 5/291:55 pm
ONT
- ORD
2 stops8h 00m
Southwest
Tue 6/27:45 am
ORD
- ONT
1 stop6h 10m
Southwest
Deal found 4/9![Southwest logo]()
$333
This United Airlines deal was found by Cheapflights users on 4/10. 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 5/27:00 am
ONT
- ORD
Nonstop3h 59m
United Airlines
Sat 5/93:35 pm
ORD
- ONT
Nonstop4h 26m
United Airlines
Deal found 4/10![United Airlines logo]()
$342
This Delta deal was found by Cheapflights users on 4/11. 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.
Sat 8/297:00 am
ONT
- MLI
1 stop7h 22m
Delta
Sun 8/305:55 am
MLI
- ONT
1 stop7h 09m
Delta
Deal found 4/11![Delta logo]()
$350
This Kiwi.com deal was found by Cheapflights users on 4/12. 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 5/27:44 pm
ONT
- RFD
1 stop14h 16m
Multiple Airlines
Wed 5/62:51 pm
RFD
- ONT
2 stops26h 18m
Multiple Airlines
Deal found 4/12![Multiple Airlines logo]()
$360
This Southwest deal was found by Cheapflights users on 4/12. 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 5/276:55 am
ONT
- MDW
2 stops7h 40m
Southwest
Mon 6/16:55 am
MDW
- ONT
1 stop6h 00m
Southwest
Deal found 4/12![Southwest logo]()
$339
This United Airlines deal was found by Cheapflights users on 4/12. 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 5/61:40 pm
ONT
- ORD
1 stop7h 18m
United Airlines
Sat 5/93:35 pm
ORD
- ONT
Nonstop4h 26m
United Airlines
Deal found 4/12![United Airlines logo]()
$351
This Southwest deal was found by Cheapflights users on 4/10. 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 5/211:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Sat 5/910:15 am
MDW
- ONT
2 stops8h 30m
Southwest
Deal found 4/10![Southwest logo]()
$342
This Kiwi.com deal was found by Cheapflights users on 4/12. 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 5/27:44 pm
ONT
- RFD
1 stop14h 16m
Multiple Airlines
Fri 5/88:35 pm
RFD
- ONT
2 stops24h 57m
Multiple Airlines
Deal found 4/12![Multiple Airlines logo]()
$403
This Delta deal was found by Cheapflights users on 4/9. 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 6/105:59 pm
ONT
- MDW
2 stops12h 38m
Delta
Mon 6/151:16 pm
MDW
- ONT
2 stops11h 25m
Delta
Deal found 4/9![Delta logo]()
$404
This United Airlines deal was found by Cheapflights users on 4/12. 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 5/191:30 pm
ONT
- ORD
1 stop9h 29m
United Airlines
Tue 5/268:13 pm
ORD
- ONT
Nonstop4h 33m
United Airlines
Deal found 4/12![United Airlines logo]()
$394
This Alaska Airlines deal was found by Cheapflights users on 4/11. 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.
Fri 8/75:32 pm
ONT
- ORD
1 stop9h 28m
Alaska Airlines
Wed 8/126:00 am
ORD
- ONT
1 stop9h 09m
Alaska Airlines
Deal found 4/11![Alaska Airlines logo]()
$479
This American Airlines deal was found by Cheapflights users on 4/8. 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 5/139:24 am
ONT
- PIA
2 stops12h 13m
American Airlines
Wed 5/2012:12 pm
PIA
- ONT
2 stops8h 18m
American Airlines
Deal found 4/8![American Airlines logo]()
$495
This Kiwi.com deal was found by Cheapflights users on 4/8. 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 7/151:27 pm
ONT
- RFD
1 stop20h 57m
Multiple Airlines
Sun 7/191:14 pm
RFD
- ONT
1 stop8h 34m
Multiple Airlines
Deal found 4/8![Multiple Airlines logo]()
$412
This Delta deal was found by Cheapflights users on 4/8. 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.
Mon 5/410:15 pm
ONT
- STL
1 stop8h 15m
Delta
Tue 5/126:00 am
STL
- ONT
1 stop6h 57m
Delta
Deal found 4/8![Delta logo]()
$415
This American Airlines deal was found by Cheapflights users on 4/8. 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.
Thu 6/42:18 pm
ONT
- EVV
1 stop7h 13m
American Airlines
Sat 6/65:30 pm
EVV
- ONT
1 stop7h 08m
American Airlines
Deal found 4/8![American Airlines logo]()
$499
This Kiwi.com deal was found by Cheapflights users on 4/12. 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 5/27:44 pm
ONT
- RFD
1 stop14h 16m
Multiple Airlines
Mon 5/48:35 pm
RFD
- ONT
2 stops29h 14m
Multiple Airlines
Deal found 4/12![Multiple Airlines logo]()
$428
This United Airlines deal was found by Cheapflights users on 4/12. 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 7/256:30 am
ONT
- MLI
1 stop6h 42m
United Airlines
Sat 8/83:52 pm
MLI
- ONT
1 stop8h 59m
United Airlines
Deal found 4/12![United Airlines logo]()
$431
This Delta deal was found by Cheapflights users on 4/10. 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.
Sat 5/236:00 am
ONT
- STL
1 stop5h 32m
Delta
Wed 6/311:25 am
STL
- ONT
2 stops14h 09m
Delta
Deal found 4/10![Delta logo]()
$435
This Southwest deal was found by Cheapflights users on 4/10. 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 5/1611:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Tue 5/1911:00 am
MDW
- ONT
Nonstop4h 15m
Southwest
Deal found 4/10![Southwest logo]()
$452
This United Airlines deal was found by Cheapflights users on 4/9. 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 8/56:30 am
ONT
- MLI
1 stop8h 28m
United Airlines
Sat 8/1510:41 am
MLI
- ONT
2 stops12h 11m
United Airlines
Deal found 4/9![United Airlines logo]()
$436
This Delta deal was found by Cheapflights users on 4/11. 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 4/2910:15 pm
ONT
- MDW
1 stop9h 41m
Delta
Wed 5/612:52 pm
MDW
- ONT
1 stop10h 08m
Delta
Deal found 4/11![Delta logo]()
$438
Last-minute flights from Ontario to IllinoisDiscover last-minute flight deals from Ontario to Illinois. Data last updated April 13, 2026 and is based on user searches.
Discover last-minute flight deals from Ontario to Illinois. Data last updated April 13, 2026 and is based on user searches.
This Kiwi.com deal was found by Cheapflights users on 4/9. 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 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Sun 5/1012:36 pm
STL
- ONT
1 stop21h 13m
Frontier
Deal found 4/9![Frontier logo]()
$168
This CheapOair deal was found by Cheapflights users on 4/8. 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.
Wed 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Fri 5/159:18 pm
STL
- ONT
1 stop19h 51m
Frontier
Deal found 4/8![Frontier logo]()
$171
This Kiwi.com deal was found by Cheapflights users on 4/8. 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 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Wed 5/66:51 pm
STL
- ONT
2 stops17h 14m
Frontier
Deal found 4/8![Frontier logo]()
$177
This Gotogate deal was found by Cheapflights users on 4/10. 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.
Thu 4/305:43 pm
ONT
- STL
1 stop23h 38m
Frontier
Mon 5/49:55 pm
STL
- ONT
1 stop19h 49m
Frontier
Deal found 4/10![Frontier logo]()
$180
This Kiwi.com deal was found by Cheapflights users on 4/11. 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 5/15:33 pm
ONT
- STL
1 stop23h 59m
Frontier
Tue 5/56:51 pm
STL
- ONT
1 stop22h 53m
Frontier
Deal found 4/11![Frontier logo]()
$175
This Delta deal was found by Cheapflights users on 4/12. 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.
Sat 5/212:49 pm
ONT
- MDW
1 stop7h 39m
Delta
Tue 5/51:24 pm
MDW
- ONT
2 stops9h 36m
Delta
Deal found 4/12![Delta logo]()
$254
This Frontier deal was found by Cheapflights users on 4/11. 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 5/48:59 pm
ONT
- STL
1 stop19h 07m
Frontier
Sun 5/1012:36 pm
STL
- ONT
1 stop21h 13m
Frontier
Deal found 4/11![Frontier logo]()
$162
This Frontier deal was found by Cheapflights users on 4/8. 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 5/88:44 am
ONT
- STL
1 stop9h 39m
Frontier
Thu 5/1412:36 pm
STL
- ONT
1 stop8h 56m
Frontier
Deal found 4/8![Frontier logo]()
$160
This Booking.com deal was found by Cheapflights users on 4/10. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 5/1111:36 am
ONT
- STL
1 stop28h 30m
Frontier
Tue 5/196:51 pm
STL
- ONT
1 stop22h 53m
Frontier
Deal found 4/10![Frontier logo]()
$172
This Booking.com deal was found by Cheapflights users on 4/8. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 5/238:43 am
ONT
- STL
1 stop8h 48m
Frontier
Mon 5/259:06 pm
STL
- ONT
1 stop12h 58m
Frontier
Deal found 4/8![Frontier logo]()
$167
This Frontier deal was found by Cheapflights users on 4/10. 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 5/238:43 am
ONT
- STL
1 stop8h 48m
Frontier
Sat 6/68:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 4/10![Frontier logo]()
$185
This Trip.com deal was found by Cheapflights users on 4/12. 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 5/276:00 am
ONT
- STL
1 stop11h 23m
Frontier
Sun 6/78:08 pm
STL
- ONT
1 stop15h 57m
Frontier
Deal found 4/12![Frontier logo]()
$174
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 April 13, 2026.
Search for one-way flight options from Ontario to Illinois. Find affordable one-way fares based on user searches. Data last updated April 13, 2026.
This Trip.com deal was found by Cheapflights users on 4/12. 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 5/66:00 am
ONT
- ORD
1 stop12h 32m
Frontier
Deal found 4/12![Frontier logo]()
$60
This Kiwi.com deal was found by Cheapflights users on 4/9. 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 4/2912:59 am
ONT
- STL
1 stop16h 22m
Frontier
Deal found 4/9![Frontier logo]()
$62
This Trip.com deal was found by Cheapflights users on 4/9. 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 5/58:06 pm
ONT
- ORD
1 stop24h 55m
Frontier
Deal found 4/9![Frontier logo]()
$66
This Trip.com deal was found by Cheapflights users on 4/8. 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.
Sun 5/312:59 am
ONT
- STL
1 stop16h 33m
Frontier
Deal found 4/8![Frontier logo]()
$67
This Kiwi.com deal was found by Cheapflights users on 4/8. 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 5/128:06 pm
ONT
- ORD
1 stop24h 55m
Frontier
Deal found 4/8![Frontier logo]()
$70
This Trip.com deal was found by Cheapflights users on 4/12. 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.
Sat 5/166:00 am
ONT
- ORD
1 stop12h 32m
Frontier
Deal found 4/12![Frontier logo]()
$74
This Super.com deal was found by Cheapflights users on 4/12. 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.
Sat 5/169:15 am
ONT
- STL
1 stop6h 49m
Frontier
Deal found 4/12![Frontier logo]()
$79
This Super.com deal was found by Cheapflights users on 4/8. 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.
Sat 5/212:59 am
ONT
- ORD
1 stop6h 46m
Frontier
Deal found 4/8![Frontier logo]()
$79
This Super.com deal was found by Cheapflights users on 4/8. 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.
Wed 4/297:44 pm
ONT
- STL
1 stop23h 16m
Frontier
Deal found 4/8![Frontier logo]()
$85
This Super.com deal was found by Cheapflights users on 4/8. 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 5/88:06 pm
ONT
- ORD
1 stop24h 55m
Frontier
Deal found 4/8![Frontier logo]()
$85
This Booking.com deal was found by Cheapflights users on 4/9. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 5/1811:36 am
ONT
- STL
1 stop28h 30m
Frontier
Deal found 4/9![Frontier logo]()
$86
This CheapOair deal was found by Cheapflights users on 4/8. 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 5/18:26 am
ONT
- ORD
1 stop27h 56m
Frontier
Deal found 4/8![Frontier logo]()
$86
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 April 13, 2026.
Most accurate provider | FlightHub 3 stars |
|---|---|
Most trusted provider | FlightHub 3 stars |
Round-trip from | $160 (Frontier) |
One-way from | $60 (Trip.com) |
Popular in | February |
Cheapest in | September |
Average price | $314 |
Good round-trip deal | $382 or less |
Good one-way deal | $209 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 April 13, 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
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 6/18
11:43 am-7:36 pm
1 stop5h 53m
Lambert-St Louis
Sun 6/21
8:21 pm-7:48 pm
1 stop25h 27m
$261
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 6/24
6:00 am-7:23 pm
1 stop11h 23m
Lambert-St Louis
Sun 6/28
8:21 pm-7:48 pm
1 stop25h 27m
$281
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Thu 5/28
5:50 pm-8:42 am
2 stops12h 52m
Chicago Midway
Thu 6/4
1:22 pm-11:34 pm
2 stops12h 12m
$292
OntarioChicago
ONT - ORD
ONTORD
Ontario
Thu 5/7
7:00 am-1:03 pm
Nonstop4h 03m
Chicago O'Hare Intl
Wed 5/13
8:09 pm-10:35 pm
Nonstop4h 26m
$296
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 6/25
3:34 pm-7:36 pm
1 stop26h 02m
Lambert-St Louis
Mon 6/29
8:21 pm-3:09 pm
1 stop20h 48m
$301
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Fri 5/1
11:55 pm-5:40 am
Nonstop3h 45m
Chicago Midway
Tue 5/5
2:55 pm-9:45 pm
1 stop8h 50m
$324
OntarioChicago
ONT - RFD
ONTRFD
Ontario
Wed 4/29
7:44 pm-12:00 pm
1 stop14h 16m
Chicago Greater Rockford
Sun 5/3
12:50 pm-8:04 am
1 stop21h 14m
$324
OntarioChicago
ONT - ORD
ONTORD
Ontario
Fri 5/29
1:55 pm-11:55 pm
2 stops8h 00m
Chicago O'Hare Intl
Tue 6/2
7:45 am-11:55 am
1 stop6h 10m
$333
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Wed 5/27
6:55 am-4:35 pm
2 stops7h 40m
Chicago Midway
Mon 6/1
6:55 am-10:55 am
1 stop6h 00m
$339
OntarioChicago
ONT - ORD
ONTORD
Ontario
Sat 5/2
7:00 am-12:59 pm
Nonstop3h 59m
Chicago O'Hare Intl
Sat 5/9
3:35 pm-6:01 pm
Nonstop4h 26m
$342
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-ORD
ONT-STL
ONT-MDW
ONT-RFD
ONT-EVV
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-ORD
ONT-STL
ONT-MDW
ONT-RFD
What is the cheapest month to book a flight from Ontario to Illinois?
Currently, April is the cheapest month in which you can book a flight from Ontario to Illinois (average of $96). Flying from Ontario to Illinois in February is currently the most expensive (average of $198). 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 April 13, 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 April 13, 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.
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Overall
8.0
Boarding
8.1
Food
7.0
Entertainment
7.5
Comfort
8.0
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.
Browse thousands of different options on Cheapflights for your next trip
Toggle through the tabs below to find thousands of options on Cheapflights for your next trip.
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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 April 13, 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 April 13, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$98 | Average$241 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$225 | Average$466 | FlexibilityNo cancel fee | On-time69% | |
| Cheapest$237 | Average$374 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$256 | Average$416 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$288 | Average$528 | FlexibilityNo cancel fee | On-time71% |