$97+ 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 7/21. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Jul 9 — Jul 161
Round-trip
1 adult, Economy
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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 June 9, 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 June 9, 2026.
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Tue 8/48:08 pm
STL
- ONT
1 stop29h 42m
Frontier
Deal found 6/6![Frontier logo]()
$236
This Frontier deal was found by Cheapflights users on 6/9. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/196:00 am
ONT
- STL
1 stop11h 23m
Frontier
Tue 9/18:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 6/9![Frontier logo]()
$244
This Booking.com deal was found by Cheapflights users on 6/9. 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.
Thu 8/611:47 am
ONT
- STL
1 stop28h 28m
Frontier
Wed 8/128:08 pm
STL
- ONT
1 stop15h 56m
Frontier
Deal found 6/9![Frontier logo]()
$249
This Kiwi.com deal was found by Cheapflights users on 6/4. 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 9/222:55 pm
ONT
- STL
2 stops16h 45m
Frontier
Sat 9/2612:46 pm
STL
- ONT
1 stop10h 08m
Frontier
Deal found 6/4![Frontier logo]()
$252
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Mon 8/37:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/6![Frontier logo]()
$259
This CheapOair deal was found by Cheapflights users on 6/8. 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 8/1410:49 am
ONT
- STL
1 stop6h 34m
Frontier
Mon 8/177:10 pm
STL
- ONT
1 stop21h 59m
Frontier
Deal found 6/8![Frontier logo]()
$260
This Expedia deal was found by Cheapflights users on 6/5. 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 8/183:34 pm
ONT
- STL
1 stop24h 34m
Frontier
Sat 8/228:08 pm
STL
- ONT
1 stop15h 57m
Frontier
Deal found 6/5![Frontier logo]()
$264
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/211:38 pm
ONT
- STL
1 stop26h 27m
Frontier
Wed 7/298:08 pm
STL
- ONT
1 stop15h 56m
Frontier
Deal found 6/6![Frontier logo]()
$265
This Booking.com deal was found by Cheapflights users on 6/8. 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.
Wed 7/81:38 pm
ONT
- STL
1 stop26h 37m
Frontier
Tue 7/147:03 pm
STL
- ONT
1 stop22h 11m
Frontier
Deal found 6/8![Frontier logo]()
$266
This Kiwi.com deal was found by Cheapflights users on 6/9. 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.
Mon 8/33:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Fri 8/77:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/9![Frontier logo]()
$269
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Sun 8/27:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/6![Frontier logo]()
$271
This Frontier deal was found by Cheapflights users on 6/8. 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.
Tue 8/2510:50 am
ONT
- STL
1 stop6h 33m
Frontier
Wed 8/268:08 pm
STL
- ONT
1 stop5h 41m
Frontier
Deal found 6/8![Frontier logo]()
$273
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 June 9, 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 June 9, 2026.
This Delta deal was found by Cheapflights users on 6/5. 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 10/296:00 am
ONT
- MDW
2 stops13h 45m
Delta
Mon 11/212:30 pm
MDW
- ONT
2 stops12h 13m
Delta
Deal found 6/5![Delta logo]()
$311
This Southwest deal was found by Cheapflights users on 6/8. 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.
Thu 9/312:00 pm
ONT
- STL
2 stops9h 05m
Southwest
Tue 9/85:30 pm
STL
- ONT
1 stop6h 35m
Southwest
Deal found 6/8![Southwest logo]()
$322
This Booking.com deal was found by Cheapflights users on 6/4. 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.
Thu 8/1310:49 am
ONT
- STL
1 stop6h 34m
Frontier
Sun 8/167:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/4![Frontier logo]()
$325
This Kiwi.com deal was found by Cheapflights users on 6/7. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/51:38 pm
ONT
- RFD
1 stop20h 56m
Multiple Airlines
Sun 8/91:24 pm
RFD
- ONT
1 stop20h 39m
Multiple Airlines
Deal found 6/7![Multiple Airlines logo]()
$380
This United Airlines deal was found by Cheapflights users on 6/8. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 8/259:15 am
ONT
- STL
1 stop6h 49m
United Airlines
Wed 8/261:36 pm
STL
- ONT
2 stops8h 25m
United Airlines
Deal found 6/8![United Airlines logo]()
$410
This American Airlines deal was found by Cheapflights users on 6/5. 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 7/2912:35 pm
ONT
- MLI
1 stop8h 55m
American Airlines
Tue 8/44:20 pm
MLI
- ONT
1 stop8h 14m
American Airlines
Deal found 6/5![American Airlines logo]()
$459
This Alaska Airlines deal was found by Cheapflights users on 6/9. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/155:54 pm
ONT
- MLI
2 stops15h 29m
Alaska Airlines
Tue 7/2111:53 am
MLI
- ONT
2 stops13h 18m
Alaska Airlines
Deal found 6/9![Alaska Airlines logo]()
$641
This Southwest deal was found by Cheapflights users on 6/5. 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 10/285:30 am
ONT
- MDW
1 stop6h 05m
Southwest
Tue 11/34:00 pm
MDW
- ONT
Nonstop4h 15m
Southwest
Deal found 6/5![Southwest logo]()
$333
This CheapOair deal was found by Cheapflights users on 6/4. 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 8/138:17 am
ONT
- MDW
1 stop10h 15m
Frontier
Sun 8/169:27 pm
MDW
- ONT
1 stop13h 14m
Frontier
Deal found 6/4![Frontier logo]()
$335
This Delta deal was found by Cheapflights users on 6/9. 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.
Tue 9/227:05 am
ONT
- MDW
1 stop7h 06m
Delta
Mon 9/281:00 pm
MDW
- ONT
2 stops12h 37m
Delta
Deal found 6/9![Delta logo]()
$376
This Frontier deal was found by Cheapflights users on 6/4. 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 7/86:00 am
ONT
- STL
1 stop11h 23m
Frontier
Thu 7/98:08 pm
STL
- ONT
1 stop5h 42m
Frontier
Deal found 6/4![Frontier logo]()
$345
This Southwest deal was found by Cheapflights users on 6/5. 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 8/111:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Tue 8/46:00 am
MDW
- ONT
1 stop8h 30m
Southwest
Deal found 6/5![Southwest logo]()
$353
This Kiwi.com deal was found by Cheapflights users on 6/9. 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.
Thu 10/2211:16 am
ONT
- RFD
1 stop6h 14m
Multiple Airlines
Sun 10/258:53 pm
RFD
- ONT
1 stop21h 17m
Multiple Airlines
Deal found 6/9![Multiple Airlines logo]()
$427
This United Airlines deal was found by Cheapflights users on 6/4. 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 10/276:53 pm
ONT
- MLI
2 stops13h 21m
United Airlines
Sat 10/315:42 pm
MLI
- ONT
1 stop6h 44m
United Airlines
Deal found 6/4![United Airlines logo]()
$436
This Southwest deal was found by Cheapflights users on 6/5. 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 10/2911:55 pm
ONT
- MDW
Nonstop3h 50m
Southwest
Mon 11/25:10 am
MDW
- ONT
1 stop7h 40m
Southwest
Deal found 6/5![Southwest logo]()
$369
This Delta deal was found by Cheapflights users on 6/9. 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.
Thu 9/246:00 pm
ONT
- MDW
2 stops12h 50m
Delta
Mon 9/281:47 pm
MDW
- ONT
2 stops11h 50m
Delta
Deal found 6/9![Delta logo]()
$426
This United Airlines deal was found by Cheapflights users on 6/8. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/267:00 am
ONT
- ORD
Nonstop4h 10m
United Airlines
Mon 8/318:06 pm
ORD
- ONT
Nonstop4h 29m
United Airlines
Deal found 6/8![United Airlines logo]()
$443
This American Airlines deal was found by Cheapflights users on 6/7. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 7/115:34 am
ONT
- PIA
1 stop8h 18m
American Airlines
Mon 7/134:43 pm
PIA
- ONT
1 stop7h 49m
American Airlines
Deal found 6/7![American Airlines logo]()
$508
This Delta deal was found by Cheapflights users on 6/9. 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.
Sun 9/135:05 pm
ONT
- STL
1 stop5h 31m
Delta
Thu 9/178:00 am
STL
- ONT
1 stop6h 10m
Delta
Deal found 6/9![Delta logo]()
$433
This United Airlines deal was found by Cheapflights users on 6/9. 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.
Tue 6/301:50 pm
ONT
- ORD
1 stop9h 09m
United Airlines
Wed 7/18:18 pm
ORD
- ONT
Nonstop4h 33m
United Airlines
Deal found 6/9![United Airlines logo]()
$449
This Southwest deal was found by Cheapflights users on 6/6. 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 7/2111:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Tue 7/283:50 pm
MDW
- ONT
Nonstop4h 05m
Southwest
Deal found 6/6![Southwest logo]()
$427
This Delta deal was found by Cheapflights users on 6/8. 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.
Wed 7/15:21 pm
ONT
- STL
1 stop5h 22m
Delta
Fri 7/37:55 pm
STL
- ONT
1 stop5h 54m
Delta
Deal found 6/8![Delta logo]()
$451
This United Airlines deal was found by Cheapflights users on 6/6. 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 7/46:10 am
ONT
- PIA
1 stop8h 48m
United Airlines
Fri 7/105:43 pm
PIA
- ONT
1 stop7h 08m
United Airlines
Deal found 6/6![United Airlines logo]()
$459
This Southwest deal was found by Cheapflights users on 6/8. 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.
Wed 7/1511:55 pm
ONT
- MDW
Nonstop3h 45m
Southwest
Wed 7/223:50 pm
MDW
- ONT
Nonstop4h 05m
Southwest
Deal found 6/8![Southwest logo]()
$427
This Delta deal was found by Cheapflights users on 6/8. 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.
Tue 7/79:40 am
ONT
- ORD
1 stop7h 17m
Delta
Tue 7/213:55 pm
ORD
- ONT
2 stops9h 53m
Delta
Deal found 6/8![Delta logo]()
$452
This American Airlines deal was found by Cheapflights users on 6/9. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 7/71:11 pm
ONT
- SPI
2 stops8h 58m
American Airlines
Mon 7/132:55 pm
SPI
- ONT
2 stops8h 48m
American Airlines
Deal found 6/9![American Airlines logo]()
$609
This United Airlines deal was found by Cheapflights users on 6/4. 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 10/276:53 pm
ONT
- PIA
2 stops13h 28m
United Airlines
Sat 10/311:20 pm
PIA
- ONT
2 stops10h 01m
United Airlines
Deal found 6/4![United Airlines logo]()
$459
This Southwest deal was found by Cheapflights users on 6/9. 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.
Sun 9/1310:10 am
ONT
- STL
2 stops7h 45m
Southwest
Thu 9/173:45 pm
STL
- ONT
1 stop6h 35m
Southwest
Deal found 6/9![Southwest logo]()
$429
This United Airlines deal was found by Cheapflights users on 6/6. 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 9/57:00 am
ONT
- PIA
1 stop6h 00m
United Airlines
Sat 9/128:45 am
PIA
- ONT
2 stops13h 16m
United Airlines
Deal found 6/6![United Airlines logo]()
$464
This Southwest deal was found by Cheapflights users on 6/9. 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.
Thu 10/151:15 pm
ONT
- STL
2 stops8h 25m
Southwest
Sun 10/188:30 am
STL
- ONT
1 stop7h 10m
Southwest
Deal found 6/9![Southwest logo]()
$429
Last-minute flights from Ontario to IllinoisDiscover last-minute flight deals from Ontario to Illinois. Data last updated June 9, 2026 and is based on user searches.
Discover last-minute flight deals from Ontario to Illinois. Data last updated June 9, 2026 and is based on user searches.
This Frontier deal was found by Cheapflights users on 6/4. 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 6/243:34 pm
ONT
- ORD
1 stop11h 33m
Frontier
Tue 7/77:15 am
ORD
- ONT
1 stop9h 59m
Frontier
Deal found 6/4![Frontier logo]()
$295
This Booking.com deal was found by Cheapflights users on 6/8. 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.
Tue 6/301:33 pm
ONT
- STL
1 stop27h 18m
Frontier
Wed 7/87:03 pm
STL
- ONT
1 stop22h 51m
Frontier
Deal found 6/8![Frontier logo]()
$289
This Booking.com deal was found by Cheapflights users on 6/8. 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.
Wed 7/81:38 pm
ONT
- STL
1 stop26h 37m
Frontier
Tue 7/147:03 pm
STL
- ONT
1 stop22h 11m
Frontier
Deal found 6/8![Frontier logo]()
$266
This Frontier deal was found by Cheapflights users on 6/7. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 7/96:00 am
ONT
- STL
1 stop11h 23m
Frontier
Wed 7/158:08 pm
STL
- ONT
1 stop15h 56m
Frontier
Deal found 6/7![Frontier logo]()
$291
This Frontier deal was found by Cheapflights users on 6/8. 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.
Sat 7/116:00 am
ONT
- STL
1 stop11h 23m
Frontier
Tue 7/148:08 pm
STL
- ONT
1 stop5h 42m
Frontier
Deal found 6/8![Frontier logo]()
$283
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/211:38 pm
ONT
- STL
1 stop26h 27m
Frontier
Wed 7/298:08 pm
STL
- ONT
1 stop15h 56m
Frontier
Deal found 6/6![Frontier logo]()
$265
This Frontier deal was found by Cheapflights users on 6/9. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 7/273:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Tue 8/47:03 pm
STL
- ONT
1 stop22h 11m
Frontier
Deal found 6/9![Frontier logo]()
$281
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Tue 8/48:08 pm
STL
- ONT
1 stop29h 42m
Frontier
Deal found 6/6![Frontier logo]()
$236
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Mon 8/37:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/6![Frontier logo]()
$259
This Kiwi.com deal was found by Cheapflights users on 6/6. 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 7/283:40 pm
ONT
- STL
1 stop24h 25m
Frontier
Fri 7/317:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/6![Frontier logo]()
$271
This Expedia deal was found by Cheapflights users on 6/6. 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 7/281:38 pm
ONT
- STL
1 stop26h 27m
Frontier
Sat 8/17:10 pm
STL
- ONT
1 stop14h 53m
Frontier
Deal found 6/6![Frontier logo]()
$287
This Gotogate deal was found by Cheapflights users on 6/8. 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 Gotogate is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/291:38 pm
ONT
- ORD
1 stop13h 59m
Frontier
Wed 8/59:57 pm
ORD
- ONT
1 stop14h 07m
Frontier
Deal found 6/8![Frontier logo]()
$296
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 June 9, 2026.
Search for one-way flight options from Ontario to Illinois. Find affordable one-way fares based on user searches. Data last updated June 9, 2026.
This Trip.com deal was found by Cheapflights users on 6/4. 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 7/216:00 am
ONT
- ORD
1 stop12h 52m
Frontier
Deal found 6/4![Frontier logo]()
$97
This Kiwi.com deal was found by Cheapflights users on 6/9. 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.
Tue 6/303:34 pm
ONT
- STL
1 stop25h 17m
Frontier
Deal found 6/9![Frontier logo]()
$100
This Trip.com deal was found by Cheapflights users on 6/5. 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 8/256:00 am
ONT
- ORD
1 stop12h 53m
Frontier
Deal found 6/5![Frontier logo]()
$100
This Kiwi.com deal was found by Cheapflights users on 6/7. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/13:34 pm
ONT
- STL
1 stop17h 44m
Frontier
Deal found 6/7![Frontier logo]()
$103
This Trip.com deal was found by Cheapflights users on 6/4. 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 57m
Frontier
Deal found 6/4![Frontier logo]()
$105
This Trip.com deal was found by Cheapflights users on 6/8. 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.
Thu 7/303:40 pm
ONT
- STL
1 stop24h 35m
Frontier
Deal found 6/8![Frontier logo]()
$106
This Kiwi.com deal was found by Cheapflights users on 6/4. 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 8/51:38 pm
ONT
- ORD
1 stop13h 59m
Frontier
Deal found 6/4![Frontier logo]()
$109
This Kiwi.com deal was found by Cheapflights users on 6/5. 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 7/1410:49 am
ONT
- ORD
1 stop8h 03m
Frontier
Deal found 6/5![Frontier logo]()
$117
This Trip.com deal was found by Cheapflights users on 6/4. 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.
Thu 8/66:00 am
ONT
- STL
1 stop11h 23m
Frontier
Deal found 6/4![Frontier logo]()
$119
This Super.com deal was found by Cheapflights users on 6/4. 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 8/1510:49 am
ONT
- ORD
1 stop8h 03m
Frontier
Deal found 6/4![Frontier logo]()
$119
This Southwest deal was found by Cheapflights users on 6/4. 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 9/111:55 pm
ONT
- MDW
Nonstop3h 50m
Southwest
Deal found 6/4![Southwest logo]()
$120
This United Airlines deal was found by Cheapflights users on 6/4. 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 8/56:10 am
ONT
- ORD
Nonstop4h 15m
United Airlines
Deal found 6/4![United Airlines logo]()
$120
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 June 9, 2026.
Most accurate provider | FlightHub 3 stars |
|---|---|
Most trusted provider | FlightHub 3 stars |
Round-trip from | $236 (Kiwi.com) |
One-way from | $97 (Trip.com) |
Popular in | February |
Cheapest in | September |
Average price | $353 |
Good round-trip deal | $430 or less |
Good one-way deal | $218 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 June 9, 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
Thu 10/29
6:00 am-9:45 pm
2 stops13h 45m
Chicago Midway
Mon 11/2
12:30 pm-10:43 pm
2 stops12h 13m
$311
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 9/3
12:00 pm-11:05 pm
2 stops9h 05m
Lambert-St Louis
Tue 9/8
5:30 pm-10:05 pm
1 stop6h 35m
$322
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 8/13
10:49 am-7:23 pm
1 stop6h 34m
Lambert-St Louis
Sun 8/16
7:10 pm-8:03 am
1 stop14h 53m
$325
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Wed 10/28
5:30 am-1:35 pm
1 stop6h 05m
Chicago Midway
Tue 11/3
4:00 pm-6:15 pm
Nonstop4h 15m
$333
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Thu 8/13
8:17 am-8:32 pm
1 stop10h 15m
Chicago Midway
Sun 8/16
9:27 pm-8:41 am
1 stop13h 14m
$335
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 7/8
6:00 am-7:23 pm
1 stop11h 23m
Lambert-St Louis
Thu 7/9
8:08 pm-11:50 pm
1 stop5h 42m
$345
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Sat 8/1
11:55 pm-5:40 am
Nonstop3h 45m
Chicago Midway
Tue 8/4
6:00 am-12:30 pm
1 stop8h 30m
$353
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Thu 10/29
11:55 pm-5:45 am
Nonstop3h 50m
Chicago Midway
Mon 11/2
5:10 am-10:50 am
1 stop7h 40m
$369
OntarioChicago
ONT - MDW
ONTMDW
Ontario
Tue 9/22
7:05 am-4:11 pm
1 stop7h 06m
Chicago Midway
Mon 9/28
1:00 pm-11:37 pm
2 stops12h 37m
$376
OntarioChicago
ONT - RFD
ONTRFD
Ontario
Wed 8/5
1:38 pm-12:34 pm
1 stop20h 56m
Chicago Greater Rockford
Sun 8/9
1:24 pm-8:03 am
1 stop20h 39m
$380
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-BMI
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, 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 June 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 June 9, 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.
Weekly flight availability from Ontario to Illinois
Explore weekly flight availability from Ontario 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 June 9, 2026.
The most flights from ONT to USIL are scheduled on a Monday (1 on average). You will have fewer flight options on Monday, which is when the least amount of flights are scheduled (1 on average).
How much does it cost to fly round-trip from Ontario to Illinois?
How far ahead should I book a flight from Ontario to Illinois?
The best time to book flights from Ontario to Illinois is 74 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.
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 June 9, 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
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
Crew
8.6
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
Crew
8.6
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
Crew
8.6
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
Crew
8.6
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
Crew
8.6
Entertainment
7.5
Food
7.0
Boarding
8.1
Comfort
8.0
Overall
7.9
Reviews
1 / 20
8.0
ExcellentLa Tracimeldamarcos,Jun 2026
LAX - SLC
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 June 9, 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 June 9, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$117 | Average$280 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$258 | Average$434 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$260 | Average$446 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$266 | Average$469 | FlexibilityNo cancel fee | On-time69% | |
| Cheapest$288 | Average$477 | FlexibilityNo cancel fee | On-time71% |