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$71+ 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 4/8. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Feb 23 — Mar 21
Mon 2/23
Mon 3/2
1 adult, Economy
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Cheap flight deals from Ontario to Illinois

Cheapest flights from Ontario to Illinois
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 January 24, 2026.

This Kiwi.com deal was found by Cheapflights users on 1/22. Clicking the “Pick Dates” 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 2/216:00 am
ONT
-
STL
1 stop5h 56m
Frontier
Sat 2/282:51 pm
STL
-
ONT
1 stop11h 08m
Frontier
Deal found 1/22$126
This Trip.com deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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 2/258:40 am
ONT
-
STL
1 stop5h 13m
Frontier
Mon 3/210:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/23$140
This Kiwi.com deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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 2/123:24 pm
ONT
-
STL
1 stop28h 02m
Frontier
Mon 2/1610:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/23$141
This Frontier deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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 2/258:40 am
ONT
-
STL
1 stop5h 13m
Frontier
Sat 2/282:51 pm
STL
-
ONT
1 stop11h 08m
Frontier
Deal found 1/23$148
This Kiwi.com deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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 3/57:22 pm
ONT
-
ORD
1 stop8h 46m
Frontier
Wed 3/118:55 pm
ORD
-
ONT
1 stop18h 16m
Frontier
Deal found 1/23$149
This CheapOair deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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.
Sat 2/218:21 am
ONT
-
ORD
1 stop12h 56m
Frontier
Mon 2/237:19 pm
ORD
-
ONT
1 stop20h 33m
Frontier
Deal found 1/23$164
This Kiwi.com deal was found by Cheapflights users on 1/21. Clicking the “Pick Dates” 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 2/196:05 am
ONT
-
ORD
1 stop15h 09m
Frontier
Tue 2/249:05 am
ORD
-
ONT
2 stops30h 47m
Frontier
Deal found 1/21$168
This Kiwi.com deal was found by Cheapflights users on 1/23. Clicking the “Pick Dates” 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 2/218:21 am
ONT
-
ORD
1 stop12h 56m
Frontier
Sat 2/284:29 pm
ORD
-
ONT
2 stops46h 42m
Frontier
Deal found 1/23$170
This Frontier deal was found by Cheapflights users on 1/22. Clicking the “Pick Dates” 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 2/511:04 am
ONT
-
STL
1 stop8h 02m
Frontier
Sat 2/73:46 pm
STL
-
ONT
1 stop9h 38m
Frontier
Deal found 1/22$180
This CheapOair deal was found by Cheapflights users on 1/22. Clicking the “Pick Dates” 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 2/182:06 pm
ONT
-
ORD
1 stop28h 57m
Frontier
Mon 2/237:19 pm
ORD
-
ONT
1 stop20h 33m
Frontier
Deal found 1/22$180
This Kiwi.com deal was found by Cheapflights users on 1/22. Clicking the “Pick Dates” 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 2/196:05 am
ONT
-
ORD
1 stop15h 09m
Multiple Airlines
Thu 2/264:42 pm
ORD
-
ONT
2 stops40h 44m
Multiple Airlines
Deal found 1/22$182
This Frontier deal was found by Cheapflights users on 1/22. Clicking the “Pick Dates” 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 2/146:00 am
ONT
-
STL
1 stop5h 56m
Frontier
Sat 2/212:51 pm
STL
-
ONT
1 stop11h 08m
Frontier
Deal found 1/22$185

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 January 24, 2026.

Most accurate provider

Justfly.com
3 stars

Most trusted provider

Justfly.com
3 stars

Round-trip from

$126
(Kiwi.com)

One-way from

$71
(Kiwi.com)

Popular in

January

Cheapest in

September

Average price

$369

Good round-trip deal

$372 or less

Good one-way deal

$153 or less
Provider with most accurate pricing for Los Angeles-Chicago (CHI) flight deals.
Search Deals
Provider most trusted by Cheapflights users for Los Angeles-Chicago (CHI) flights.
Search Deals
From Ontario to Illinois
Search Deals
One-way flight from Ontario to Illinois
Search Deals
Highest demand for flights based on searches. 9% potential increase in price ($32 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($7 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in January 2026
Search Deals
Price to beat on a round-trip flight from Ontario to Illinois.
Search Deals
Price to beat on a one-way flight from Ontario to Illinois.
Search Deals

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 January 24, 2026.
Use the filters below to find and compare flights from Ontario to Illinois that are best for you.

Fly from

Ontario

Fly to

Illinois

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/12

3:24 pm-1:09 pm

2 stops19h 45m

Lambert-St Louis

Mon 2/16

10:11 pm-1:11 pm

1 stop17h 00m

$215

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/5

8:48 pm-8:48 pm

1 stop22h 00m

Lambert-St Louis

Sun 2/8

12:03 pm-12:20 am

1 stop14h 17m

$215

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 3/5

6:05 am-9:49 am

1 stop25h 44m

Lambert-St Louis

Tue 3/10

8:06 pm-1:28 pm

1 stop19h 22m

$225

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

3:07 pm-12:08 pm

2 stops43h 01m

Lambert-St Louis

Fri 2/6

9:43 pm-6:40 pm

1 stop22h 57m

$237

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/14

6:00 am-1:56 pm

1 stop5h 56m

Lambert-St Louis

Thu 2/19

10:11 pm-7:22 am

1 stop11h 11m

$241

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 4/25

7:30 am-9:31 pm

2 stops12h 01m

Lambert-St Louis

Tue 4/28

2:22 pm-10:37 pm

2 stops10h 15m

$256

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 4/25

5:10 am-1:08 pm

1 stop5h 58m

Lambert-St Louis

Tue 4/28

4:30 pm-8:36 pm

1 stop6h 06m

$257

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 4/25

2:08 pm-11:04 pm

1 stop6h 56m

Lambert-St Louis

Tue 4/28

8:53 am-4:22 pm

2 stops9h 29m

$262

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 3/31

5:09 pm-12:21 am

1 stop5h 12m

Lambert-St Louis

Sat 4/4

5:00 pm-10:48 pm

1 stop7h 48m

$277

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 3/31

6:00 am-1:18 pm

1 stop5h 18m

Lambert-St Louis

Wed 4/1

6:12 pm-11:51 pm

1 stop7h 39m

$277

Flights are sorted by cheapest round-trip flights first.

Deals found on 1/23

Showing 1-10 of 60 results
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6

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.
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

What is the cheapest month to book a flight from Ontario to Illinois?

Currently, March is the cheapest month in which you can book a flight from Ontario to Illinois (average of $77). Flying from Ontario to Illinois in October is currently the most expensive (average of $147). 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 January 24, 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.

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 January 24, 2026.
Read through reviews of airlines operating flights from Ontario to Illinois, such as Southwest, Delta, and United Airlines. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.
Southwest
8.0
Very good
4,268 reviews
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.
Delta
7.9
Good
8,110 reviews
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.
United Airlines
7.4
Good
9,194 reviews
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.
American Airlines
7.2
Good
11,192 reviews
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.
Frontier
5.7
Fair
3,058 reviews
Southwest
8.0
Very good
4,268 reviews

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

Overall

8.0

Crew

8.6

Reviews

1 / 20
10.0
Excellent

William Drew,Nov 2025

SJC - HNL

Flight crew was amazing! Usually they're very good on Southwest, but this crew went above and beyond. I have never ever seen so many rounds of drink service on a flight before.

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.

  • What airport do you fly from for flights from Ontario to Illinois?

    Ontario (ONT), located 3.1 mi from the city center, is the airport you fly out of when you book flights from Ontario to Illinois.

  • How long is the flight from Ontario to Illinois?

    For as low as $321, Frontier can have you in Illinois from Ontario in 8h 56m. The distance between Ontario and Illinois is about 1695 mi. Both multi-stop and nonstop flights can be found to your destination and back.

  • What are the cheapest airlines to fly from Ontario to Illinois one-way?

    $80 is the cheapest one-way deal found within the past few days, from Frontier. You may also be able to find cheap deals on United Airlines and American Airlines, with prices starting from $102 and $112, respectively.

  • What are the most popular routes from Ontario to Illinois?

    The most popular flight routes from Ontario to Illinois are Ontario - Chicago O'Hare Intl, Ontario - Chicago Midway and Ontario - Lambert-St Louis.

  • What are the cheapest flights from Ontario to Illinois?

    While on average a flight from Ontario to Illinois is generally $628, our data shows the cheapest flight currently is $101. When looking at the most popular route, (Ontario - Chicago O'Hare Intl), you can expect to pay $182 for that flight.

  • Can I find deals for flights from Ontario to Illinois that include hotel bookings?

    Yes. In addition to deals on Ontario to Illinois flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Ontario to Illinois?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Ontario to Illinois.

  • Can I find deals for business class flights from Ontario to Illinois?

    Yes. Cheapflights offers flight deals from Ontario to Illinois by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from Ontario to Illinois?

    Currently, March is the cheapest month in which you can book a flight from Ontario to Illinois (average of $77). Flying from Ontario to Illinois in October is currently the most expensive (average of $147). 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.

See more FAQs

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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.
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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 January 24, 2026.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$102Average$229FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$226Average$459FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$237Average$399FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$246Average$469FlexibilityNo cancel feeOn-time71%
DeltaCheapest$254Average$354FlexibilityNo cancel feeOn-timeN/A

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