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$69+ 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 2/21. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Jan 25 — Feb 11
Sun 1/25
Sun 2/1
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 December 26, 2025.

This CheapOair deal was found by Cheapflights users on 12/23. 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.
Wed 12/316:00 amONT - STL
1 stop8h 24mFrontier
Sun 1/410:10 pmSTL - ONT
1 stop25h 07mFrontier
Deal found 12/23$238
This CheapOair deal was found by Cheapflights users on 12/24. 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 12/316:45 amONT - ORD
1 stop15h 27mFrontier
Sun 1/410:49 pmORD - ONT
1 stop24h 28mFrontier
Deal found 12/24$238
This Kiwi.com deal was found by Cheapflights users on 12/22. 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.
Mon 12/296:00 amONT - STL
1 stop13h 25mFrontier
Mon 1/510:10 pmSTL - ONT
1 stop18h 59mFrontier
Deal found 12/22$249
This CheapOair deal was found by Cheapflights users on 12/24. 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 12/256:00 amONT - STL
1 stop8h 24mFrontier
Mon 1/510:10 pmSTL - ONT
1 stop18h 59mFrontier
Deal found 12/24$275
This Super.com deal was found by Cheapflights users on 12/24. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/316:45 amONT - ORD
1 stop15h 27mFrontier
Sat 1/38:20 amORD - ONT
1 stop8h 10mFrontier
Deal found 12/24$278
This Frontier deal was found by Cheapflights users on 12/23. 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 12/316:00 amONT - STL
1 stop8h 24mFrontier
Fri 1/27:43 pmSTL - ONT
1 stop6h 16mFrontier
Deal found 12/23$282
This Frontier deal was found by Cheapflights users on 12/24. 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 12/256:00 amONT - ORD
1 stop6h 17mFrontier
Thu 1/17:57 pmORD - ONT
1 stop13h 22mFrontier
Deal found 12/24$304
This CheapOair deal was found by Cheapflights users on 12/23. 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.
Tue 12/306:00 amONT - STL
1 stop13h 25mFrontier
Sun 1/410:10 pmSTL - ONT
1 stop21h 05mFrontier
Deal found 12/23$313
This CheapOair deal was found by Cheapflights users on 12/24. 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 12/256:00 amONT - ORD
1 stop6h 17mFrontier
Sat 1/38:20 amORD - ONT
1 stop8h 10mFrontier
Deal found 12/24$329
This CheapOair deal was found by Cheapflights users on 12/25. 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.
Mon 12/296:20 pmONT - ORD
1 stop27h 21mFrontier
Mon 1/127:50 pmORD - ONT
1 stop29h 09mFrontier
Deal found 12/25$333
This CheapOair deal was found by Cheapflights users on 12/24. 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.
Tue 12/306:00 amONT - ORD
1 stop6h 17mFrontier
Mon 1/57:00 amORD - ONT
1 stop18h 59mFrontier
Deal found 12/24$344
This Frontier deal was found by Cheapflights users on 12/24. 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 12/306:00 amONT - ORD
1 stop6h 17mFrontier
Thu 1/17:57 pmORD - ONT
1 stop13h 22mFrontier
Deal found 12/24$347

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 December 26, 2025.

Most accurate provider

Justfly.com
3 stars

Most trusted provider

Justfly.com
3 stars

Round-trip from

$159
(Kiwi.com)

One-way from

$69
(Trip.com)

Popular in

December

Cheapest in

September

Average price

$368

Good round-trip deal

$352 or less

Good one-way deal

$187 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. 10% potential increase in price ($35 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($8 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in December 2025
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 December 26, 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

Wed 1/28

7:15 am-2:46 pm

1 stop5h 31m

Lambert-St Louis

Sun 2/1

9:32 pm-2:41 pm

1 stop19h 09m

$201

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Thu 1/15

8:02 am-5:20 pm

1 stop7h 18m

Chicago Midway

Mon 1/19

9:09 pm-3:07 pm

1 stop19h 58m

$202

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/6

8:48 pm-2:46 pm

2 stops15h 58m

Lambert-St Louis

Sun 2/8

9:32 pm-12:10 pm

1 stop16h 38m

$204

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 1/1

6:45 am-10:02 am

1 stop25h 17m

Lambert-St Louis

Sun 1/4

10:10 pm-9:17 pm

1 stop25h 07m

$263

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 1/6

7:00 am-10:02 am

1 stop25h 02m

Lambert-St Louis

Fri 1/9

7:43 pm-11:56 pm

1 stop6h 13m

$270

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 1/4

6:37 pm-9:25 pm

1 stop24h 48m

Lambert-St Louis

Sun 1/11

12:37 pm-6:24 pm

1 stop7h 47m

$273

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Sun 2/8

10:18 am-11:13 pm

1 stop10h 55m

Chicago Midway

Sun 2/15

3:21 pm-1:11 pm

2 stops23h 50m

$274

OntarioChicago

ONT - ORD

ONTORD

Ontario

Sat 1/24

11:53 am-11:50 pm

1 stop9h 57m

Chicago O'Hare Intl

Mon 1/26

6:06 pm-3:08 pm

1 stop23h 02m

$284

OntarioChicago

ONT - ORD

ONTORD

Ontario

Wed 2/4

7:30 am-11:53 pm

1 stop14h 23m

Chicago O'Hare Intl

Tue 2/24

2:20 pm-10:37 pm

1 stop10h 17m

$285

OntarioChicago

ONT - ORD

ONTORD

Ontario

Tue 2/3

7:30 am-11:53 pm

1 stop14h 23m

Chicago O'Hare Intl

Wed 2/25

7:40 am-1:54 pm

1 stop8h 14m

$285

Flights are sorted by cheapest round-trip flights first.

Deals found on 12/25

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, 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 December 26, 2025.

Unlike in the morning, when flights are generally more expensive, you can save up to 42% on flights from Ontario to Illinois by exploring options for tickets in the afternoon.

What is the cheapest day to fly from Ontario to Illinois?

Use this chart to determine the cheapest time to fly round-trip from Ontario to Illinois. Price data was last updated on December 16, 2024.

Travelers seeking maximum savings on their Ontario to Illinois flight should consider departing on Thursday at noon when fares are most often at their lowest. Sunday at noon flights should be avoided if possible as fares are typically the most expensive at this time.

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 December 26, 2025.

The most flights from ONT to USIL are scheduled on a Monday (2 on average). You will have fewer flight options on Tuesday, which is when the least amount of flights are scheduled (1 on average).

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 December 26, 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
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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
4,258 reviews
Southwest
8.0
Very good
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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
8,013 reviews
Southwest
8.0
Very good
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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
9,115 reviews
Southwest
8.0
Very good
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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
11,062 reviews
Southwest
8.0
Very good
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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
5.8
Fair
3,070 reviews
Southwest
8.0
Very good
4,258 reviews

Crew

8.6

Overall

8.0

Boarding

8.1

Comfort

8.0

Entertainment

7.5

Food

7.0

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 $201, Frontier can have you in Illinois from Ontario in 5h 31m. 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?

    $79 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 $387, our data shows the cheapest flight currently is $139. When looking at the most popular route, (Ontario - Chicago O'Hare Intl), you can expect to pay $183 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 December 26, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$110Average$225FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$227Average$459FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$237Average$419FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$246Average$475FlexibilityNo cancel feeOn-time71%
DeltaCheapest$256Average$355FlexibilityNo cancel feeOn-timeN/A

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