HomeSearch by dateVacation packagesHotelsFlight dealsCar rentalTravel tips & news
Illinois

$63+ 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 3/5. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Feb 20 — Feb 271
Fri 2/20
Fri 2/27
1 adult, Economy
We work with more than 300 partners to bring you better travel deals

Find cheap flights from Ontario to Illinois with Cheapflights

1. Tell us where you want to go

Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”

2. Select your favorite providers

We find the providers serving your travel needs. Choose up to four travel providers to compare side-by-side for flights, hotels, or car rentals.

3. Compare prices and book

Review each provider’s pricing and select the best option for you! Book through your favorite provider’s website for a seamless experience.

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 21, 2026.

This Kiwi.com deal was found by Cheapflights users on 1/20. 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
Mon 2/2310:11 pm
STL
-
ONT
1 stop17h 41m
Frontier
Deal found 1/20$124
This Kiwi.com deal was found by Cheapflights users on 1/20. 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 2/267:22 pm
ONT
-
STL
1 stop24h 04m
Frontier
Sun 3/110:11 pm
STL
-
ONT
1 stop21h 37m
Frontier
Deal found 1/20$133
This Kiwi.com deal was found by Cheapflights users on 1/20. 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 2/187:17 pm
ONT
-
STL
1 stop24h 09m
Frontier
Fri 2/2010:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/20$134
This Kiwi.com deal was found by Cheapflights users on 1/20. 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.
Fri 2/209:43 pm
ONT
-
STL
1 stop18h 03m
Frontier
Mon 2/2310:11 pm
STL
-
ONT
1 stop17h 41m
Frontier
Deal found 1/20$145
This Mytrip deal was found by Cheapflights users on 1/19. 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.
Wed 2/187:17 pm
ONT
-
STL
1 stop24h 09m
Frontier
Sat 2/212:51 pm
STL
-
ONT
1 stop19h 08m
Frontier
Deal found 1/19$148
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.
Sat 3/76:15 am
ONT
-
ORD
1 stop24h 28m
Frontier
Thu 3/1210:53 am
ORD
-
ONT
1 stop15h 06m
Frontier
Deal found 1/21$163
This Frontier deal was found by Cheapflights users on 1/18. 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 1/18$164
This Kiwi.com deal was found by Cheapflights users on 1/20. 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 2/187:17 pm
ONT
-
ORD
1 stop23h 46m
Frontier
Wed 2/2511:51 am
ORD
-
ONT
2 stops23h 43m
Frontier
Deal found 1/20$164
This Mytrip deal was found by Cheapflights users on 1/20. 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.
Wed 2/187:17 pm
ONT
-
STL
1 stop24h 09m
Frontier
Mon 2/2310:11 pm
STL
-
ONT
1 stop17h 41m
Frontier
Deal found 1/20$173
This Kiwi.com deal was found by Cheapflights users on 1/20. 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 2/178:35 am
ONT
-
STL
2 stops20h 16m
Frontier
Fri 2/2010:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/20$174
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.
Sat 3/76:15 am
ONT
-
ORD
1 stop24h 28m
Frontier
Tue 3/107:00 am
ORD
-
ONT
2 stops18h 59m
Frontier
Deal found 1/21$174
This Kiwi.com deal was found by Cheapflights users on 1/19. 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.
Fri 3/66:15 am
ONT
-
STL
1 stop25h 34m
Frontier
Sun 3/89:22 pm
STL
-
ONT
1 stop12h 44m
Frontier
Deal found 1/19$175

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 21, 2026.

Most accurate provider

Justfly.com
3 stars

Most trusted provider

Justfly.com
3 stars

Round-trip from

$124
(Kiwi.com)

One-way from

$63
(Trip.com)

Popular in

January

Cheapest in

September

Average price

$369

Good round-trip deal

$352 or less

Good one-way deal

$136 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 21, 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 2/26

7:22 pm-9:26 pm

1 stop24h 04m

Lambert-St Louis

Sun 3/1

10:11 pm-5:48 pm

1 stop21h 37m

$133

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/18

7:17 pm-9:26 pm

1 stop24h 09m

Lambert-St Louis

Fri 2/20

10:11 pm-1:11 pm

1 stop17h 00m

$134

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/20

9:43 pm-5:46 pm

1 stop18h 03m

Lambert-St Louis

Mon 2/23

10:11 pm-1:52 pm

1 stop17h 41m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/3

7:15 am-2:46 pm

1 stop29h 31m

Lambert-St Louis

Fri 2/6

9:43 pm-1:34 pm

1 stop17h 51m

$185

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/19

2:08 pm-1:09 pm

1 stop21h 01m

Lambert-St Louis

Mon 2/23

10:11 pm-1:52 pm

1 stop17h 41m

$191

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/17

8:35 am-3:53 pm

1 stop29h 18m

Lambert-St Louis

Fri 2/20

10:11 pm-1:11 pm

1 stop17h 00m

$202

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/11

3:22 pm-9:26 pm

1 stop28h 04m

Lambert-St Louis

Mon 2/16

10:11 pm-1:11 pm

1 stop17h 00m

$205

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sun 2/8

9:32 pm-7:10 pm

1 stop23h 38m

$215

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Fri 2/6

9:43 pm-6:40 pm

1 stop22h 57m

$215

OntarioChicago

ONT - ORD

ONTORD

Ontario

Fri 2/20

1:18 pm-3:17 pm

1 stop23h 59m

Chicago O'Hare Intl

Mon 2/23

7:19 pm-1:52 pm

1 stop20h 33m

$215

Flights are sorted by cheapest round-trip flights first.

Deals found on 1/21

Showing 1-10 of 60 results
1
2
3
...
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 21, 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 21, 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
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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
4,266 reviews
Southwest
8.0
Very good
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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
8,089 reviews
Southwest
8.0
Very good
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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
9,191 reviews
Southwest
8.0
Very good
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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
11,174 reviews
Southwest
8.0
Very good
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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
5.7
Fair
3,057 reviews
Southwest
8.0
Very good
4,266 reviews

Boarding

8.1

Crew

8.6

Overall

8.0

Entertainment

7.5

Food

7.0

Comfort

8.0

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 $301, Frontier can have you in Illinois from Ontario in 9h 31m. The distance between Ontario and Illinois is about 1701 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 $185 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

Browse thousands of different options on Cheapflights for your next trip

Toggle through the tabs below to find thousands of options on Cheapflights for your next trip.

Alternative routes for Ontario to Illinois

See prices for flight routes from nearby airports that may be better suited for you.
Los Angeles to Seattle flights
Los Angeles to John F Kennedy Intl flights
Los Angeles to Honolulu flights
Ontario to Seattle flights
San Francisco to John F Kennedy Intl flights
San Francisco to Las Vegas flights
Los Angeles to Newark flights
San Francisco to Newark flights
Los Angeles to Las Vegas flights
San Francisco to Los Angeles flights
San Francisco to Honolulu flights
San Francisco to Ontario flights
Los Angeles to Dallas/Fort Worth flights
Los Angeles to Orlando flights
Los Angeles to LaGuardia flights
Los Angeles to Miami flights
Burbank to Las Vegas flights
Los Angeles to San Francisco flights
Los Angeles to O'Hare Intl flights
San Francisco to Dallas/Fort Worth flights
Ontario to San Francisco flights
Los Angeles to Hobby flights
Santa Ana to Las Vegas flights
Los Angeles to Denver flights
San Jose to Los Angeles flights
San Francisco to Santa Ana flights
San Francisco to Seattle flights
Santa Ana to Seattle flights
Los Angeles to New Orleans flights
San Francisco to Sky Harbor Intl flights
Los Angeles to Sky Harbor Intl flights
San Francisco to LaGuardia flights
Los Angeles to Salt Lake City flights
San Francisco to O'Hare Intl flights
Los Angeles to George Bush Intcntl flights
Los Angeles to Kahului flights
San Francisco to Denver flights
Los Angeles to Atlanta flights
San Jose to Las Vegas flights
Los Angeles to Reagan-National flights
San Francisco to Kahului flights
Los Angeles to Fort Lauderdale flights
Santa Ana to San Francisco flights
San Francisco to San Diego flights
Los Angeles to Austin flights
Los Angeles to San Jose flights
San Diego to Las Vegas flights
Oakland to Las Vegas flights
Los Angeles to Boston flights
San Jose to Seattle flights

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 21, 2026.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$102Average$225FlexibilityNo 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

100% Free

Cheapflights is completely free to use, so you can start saving the moment you arrive.

Book with Flexibility

Our users can plan ahead with confidence and find flights with no change fees

Travel Smart

Millions of people come to us for their flight needs every year. We help make travel planning easy by providing useful insights and data-driven graphs that can inform your decisions.