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$54+ Cheap flights from Ontario (ONT) to Illinois

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 9/30. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Oct 11 — Oct 181
Sat 10/11
Sat 10/18
1 adult, Economy
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Cheap flight deals from Ontario to Illinois

Keep the following information in mind while searching for Ontario to Illinois flight deals. Data was last updated September 11, 2025.

Round-trip from

$118
(Kiwi.com)

One-way from

$54
(Trip.com)

Popular in

December

Cheapest in

February

Average price

$268

Good round-trip deal

$330 or less

Good one-way deal

$196 or less
From Ontario to Illinois
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One-way flight from Ontario to Illinois
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Highest demand for flights based on searches. 8% potential increase in price ($26 potential increase over avg. RT price).
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Cheapest flight prices on average. 1% potential price decrease ($4 potential savings vs. average RT price).
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Average for round-trip flights in September 2025
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Price to beat on a round-trip flight from Ontario to Illinois.
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Price to beat on a one-way flight from Ontario to Illinois.
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Find 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 September 11, 2025.

This Kiwi.com deal was found by Cheapflights users on 9/10. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 11/106:53 amONT - STL
1 stop24h 14mFrontier
Fri 11/147:45 pmSTL - ONT
1 stop17h 25mFrontier
Deal found 9/10$118
This Cheapflightsfares deal was found by Cheapflights users on 9/8. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 11/66:00 amONT - STL
1 stop5h 57mFrontier
Sat 11/84:51 pmSTL - ONT
1 stop5h 51mFrontier
Deal found 9/8$142
This Priceline deal was found by Cheapflights users on 9/11. 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 Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/258:59 pmONT - STL
1 stop10h 07mFrontier
Tue 10/77:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/11$143
This Booking.com deal was found by Cheapflights users on 9/8. 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 9/248:59 pmONT - STL
1 stop10h 07mFrontier
Mon 9/297:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 9/8$144
This Booking.com deal was found by Cheapflights users on 9/10. 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.
Fri 9/194:08 pmONT - STL
1 stop14h 58mFrontier
Sun 9/212:38 pmSTL - ONT
1 stop25h 22mFrontier
Deal found 9/10$145
This Kiwi.com deal was found by Cheapflights users on 9/9. 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 10/296:53 amONT - STL
1 stop24h 14mFrontier
Tue 11/47:45 pmSTL - ONT
1 stop6h 05mFrontier
Deal found 9/9$149
This Flightnetwork deal was found by Cheapflights users on 9/9. 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 Flightnetwork is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 10/77:04 amONT - STL
1 stop24h 03mFrontier
Tue 10/147:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/9$151
This Cheapflightsfares deal was found by Cheapflights users on 9/9. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 10/26:00 amONT - STL
1 stop5h 53mFrontier
Tue 10/77:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/9$152
This Frontier deal was found by Cheapflights users on 9/10. 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 9/208:59 pmONT - STL
1 stop10h 07mFrontier
Thu 9/2510:49 amSTL - ONT
1 stop6h 40mFrontier
Deal found 9/10$154
This Frontier deal was found by Cheapflights users on 9/11. 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.
Fri 9/268:59 pmONT - STL
1 stop10h 07mFrontier
Sun 9/2810:39 amSTL - ONT
1 stop9h 36mFrontier
Deal found 9/11$155
This Mytrip deal was found by Cheapflights users on 9/10. 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 Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/118:00 amONT - STL
1 stop5h 56mFrontier
Mon 10/139:59 pmSTL - ONT
1 stop24h 43mFrontier
Deal found 9/10$156
This United Airlines deal was found by Cheapflights users on 9/11. 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 United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 10/17:02 amONT - ORD
Nonstop4h 03mUnited Airlines
Mon 10/67:59 pmORD - ONT
Nonstop4h 31mUnited Airlines
Deal found 9/11$179

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 September 11, 2025.
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

Sat 9/27

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Mon 9/29

7:55 pm-7:54 pm

1 stop25h 59m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/30

7:44 pm-8:12 pm

1 stop22h 28m

Lambert-St Louis

Sun 11/2

7:45 pm-11:10 am

1 stop17h 25m

$158

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 11/3

4:05 pm-9:07 am

1 stop15h 02m

Lambert-St Louis

Tue 11/4

7:45 pm-11:50 pm

1 stop6h 05m

$173

OntarioChicago

ONT - ORD

ONTORD

Ontario

Tue 10/21

7:02 am-1:05 pm

Nonstop4h 03m

Chicago O'Hare Intl

Wed 10/22

7:59 pm-10:30 pm

Nonstop4h 31m

$179

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 10/24

10:47 pm-9:07 am

2 stops8h 20m

Lambert-St Louis

Fri 10/31

8:40 pm-11:10 am

1 stop16h 30m

$180

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Sat 10/11

8:34 am-11:20 pm

1 stop12h 46m

Chicago Midway

Sun 10/19

10:30 am-5:49 pm

1 stop9h 19m

$182

OntarioChicago

ONT - ORD

ONTORD

Ontario

Sat 10/18

7:02 am-1:05 pm

Nonstop4h 03m

Chicago O'Hare Intl

Mon 10/20

7:59 pm-10:30 pm

Nonstop4h 31m

$188

OntarioChicago

ONT - ORD

ONTORD

Ontario

Fri 10/17

12:32 pm-12:44 am

1 stop10h 12m

Chicago O'Hare Intl

Sun 10/19

9:54 pm-7:47 am

1 stop11h 53m

$188

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 10/15

6:53 am-9:07 am

1 stop24h 14m

Lambert-St Louis

Sat 10/18

4:51 pm-8:42 pm

1 stop5h 51m

$189

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 10/11

8:00 am-3:56 pm

1 stop5h 56m

Lambert-St Louis

Sat 10/18

4:51 pm-8:42 pm

1 stop5h 51m

$189

Flights are sorted by cheapest round-trip flights first.

Deals found on 9/11

Showing 1-10 of 60 results
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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, August is the cheapest month in which you can book a flight from Ontario to Illinois (average of $245). Flying from Ontario to Illinois in March is currently the most expensive (average of $321). 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 September 11, 2025.

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 September 11, 2025.
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
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Southwest
8.0
Very good
4,248 reviews
Southwest
8.0
Very good
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Delta
8.0
Very good
7,960 reviews
Southwest
8.0
Very good
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
United Airlines
7.4
Good
8,937 reviews
Southwest
8.0
Very good
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
American Airlines
7.2
Good
10,000 reviews
Southwest
8.0
Very good
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Frontier
5.8
Fair
3,177 reviews
Southwest
8.0
Very good
4,248 reviews

Boarding

8.1

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Comfort

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.

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 $179, Frontier can have you in Illinois from Ontario in 4h 03m. 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?

    $77 is the cheapest one-way deal found within the past few days, from Frontier. You may also be able to find cheap deals on Southwest and United Airlines, with prices starting from $92 and $98, 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 $752, our data shows the cheapest flight currently is $156. When looking at the most popular route, (Ontario - Chicago O'Hare Intl), you can expect to pay $149 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, August is the cheapest month in which you can book a flight from Ontario to Illinois (average of $245). Flying from Ontario to Illinois in March is currently the most expensive (average of $321). 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.

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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 6 airlines flying from Ontario to Illinois

Discover the top 6 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 September 11, 2025.
AirlineCheapestAverageFlexibilityOn-time
Spirit AirlinesCheapest$99Average$145FlexibilityNo cancel feeOn-time65%
FrontierCheapest$108Average$180FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$227Average$488FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$237Average$434FlexibilityNo cancel feeOn-time63%
DeltaCheapest$241Average$411FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$246Average$507FlexibilityNo cancel feeOn-time71%

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