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$72+ 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 10/18. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Oct 17 — Oct 241
Fri 10/17
Fri 10/24
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 17, 2025.

Round-trip from

$143
(Mytrip)

One-way from

$72
(Cheapflightsfares)

Popular in

December

Cheapest in

February

Average price

$279

Good round-trip deal

$343 or less

Good one-way deal

$198 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. 9% potential increase in price ($28 potential increase over avg. RT price).
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Cheapest flight prices on average. 1% potential price decrease ($5 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 17, 2025.

This Mytrip deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 10/310:28 pmONT - STL
1 stop15h 35mFrontier
Sun 10/57:55 pmSTL - ONT
1 stop13h 58mFrontier
Deal found 9/15$143
This Frontier deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/188:00 amONT - STL
1 stop5h 56mFrontier
Thu 10/2310:17 amSTL - ONT
1 stop7h 15mFrontier
Deal found 9/16$144
This Booking.com deal was found by Cheapflights users on 9/14. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/238:59 pmONT - STL
1 stop10h 07mFrontier
Tue 9/307:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 9/14$145
This Booking.com deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com 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
Mon 9/299:29 pmSTL - ONT
1 stop26h 27mFrontier
Deal found 9/15$146
This Cheapflightsfares deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 11/88:00 amONT - STL
1 stop5h 56mFrontier
Tue 11/117:45 pmSTL - ONT
1 stop6h 05mFrontier
Deal found 9/15$155
This Booking.com deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 9/288:59 pmONT - STL
1 stop10h 07mFrontier
Tue 9/307:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 9/15$157
This Trip.com deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 10/96:05 amONT - STL
1 stop27h 38mFrontier
Tue 10/147:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/16$158
This Trip.com deal was found by Cheapflights users on 9/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 11/1311:59 amONT - MDW
1 stop6h 45mFrontier
Sun 11/166:30 amMDW - ONT
1 stop14h 19mFrontier
Deal found 9/17$173
This Booking.com deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 9/2912:13 pmONT - MDW
1 stop6h 39mFrontier
Thu 10/26:30 amMDW - ONT
1 stop14h 05mFrontier
Deal found 9/16$174
This Booking.com deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 9/268:59 pmONT - ORD
1 stop22h 29mFrontier
Tue 9/307:20 amORD - ONT
1 stop14h 34mFrontier
Deal found 9/16$174
This Frontier deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/308:59 pmONT - STL
1 stop10h 07mFrontier
Wed 10/87:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/16$175
This Booking.com deal was found by Cheapflights users on 9/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/238:59 pmONT - STL
1 stop10h 07mFrontier
Fri 9/269:35 pmSTL - ONT
1 stop17h 08mFrontier
Deal found 9/17$178

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 17, 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

Thu 11/13

6:00 am-1:57 pm

1 stop5h 57m

Lambert-St Louis

Mon 11/17

7:45 pm-11:50 pm

1 stop6h 05m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 10/14

7:04 am-9:07 am

1 stop24h 03m

Lambert-St Louis

Tue 10/21

7:52 pm-11:50 pm

1 stop5h 58m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 10/18

8:00 am-3:56 pm

1 stop5h 56m

Lambert-St Louis

Tue 10/21

7:52 pm-11:50 pm

1 stop5h 58m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/8

8:00 am-3:56 pm

1 stop5h 56m

Lambert-St Louis

Tue 11/11

7:45 pm-11:50 pm

1 stop6h 05m

$156

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/9

6:05 am-11:43 am

1 stop27h 38m

Lambert-St Louis

Tue 10/14

7:52 pm-11:50 pm

1 stop5h 58m

$158

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 10/24

10:47 pm-3:56 pm

1 stop15h 09m

Lambert-St Louis

Sun 10/26

7:52 pm-9:35 am

1 stop15h 43m

$190

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 10/22

6:53 am-9:07 am

1 stop24h 14m

Lambert-St Louis

Sun 10/26

10:17 am-3:32 pm

1 stop7h 15m

$201

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Sat 10/11

8:34 am-11:20 pm

1 stop12h 46m

Chicago Midway

Mon 10/13

9:00 am-4:28 pm

1 stop9h 28m

$223

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Thu 10/23

10:30 am-11:20 pm

2 stops10h 50m

Chicago Midway

Mon 10/27

9:00 am-4:28 pm

1 stop9h 28m

$230

OntarioChicago

ONT - RFD

ONTRFD

Ontario

Thu 9/25

9:16 am-7:47 pm

1 stop8h 31m

Chicago Greater Rockford

Sun 9/28

8:37 pm-7:17 am

1 stop12h 40m

$270

Flights are sorted by cheapest round-trip flights first.

Deals found on 9/17

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 17, 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 17, 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
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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
4,242 reviews
Southwest
8.0
Very good
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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
7,961 reviews
Southwest
8.0
Very good
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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
8,926 reviews
Southwest
8.0
Very good
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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
3,173 reviews
Southwest
8.0
Very good
4,242 reviews

Entertainment

7.5

Food

7.0

Overall

8.0

Comfort

8.0

Crew

8.6

Boarding

8.1

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 $143, Frontier can have you in Illinois from Ontario in 5h 57m. The distance between Ontario and Illinois is about 1541 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?

    $78 is the cheapest one-way deal found within the past few days, from Frontier. You may also be able to find cheap deals on Delta and United Airlines, with prices starting from $147 and $161, 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 $805, 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 $148 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 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 September 17, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$108Average$184FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$227Average$481FlexibilityNo cancel feeOn-time69%
DeltaCheapest$236Average$409FlexibilityNo cancel feeOn-timeN/A
SouthwestCheapest$237Average$437FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$246Average$513FlexibilityNo cancel feeOn-time71%

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