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$67+ 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 2/25. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Feb 28 — Mar 71
Sat 2/28
Sat 3/7
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 29, 2026.

This Frontier deal was found by Cheapflights users on 1/26. 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 1/26$148
This Booking.com deal was found by Cheapflights users on 1/26. 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 2/258:40 am
ONT
-
STL
1 stop5h 13m
Frontier
Wed 3/45:18 pm
STL
-
ONT
1 stop6h 16m
Frontier
Deal found 1/26$149
This Kiwi.com deal was found by Cheapflights users on 1/27. 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 2/288:21 am
ONT
-
ORD
1 stop12h 56m
Frontier
Sat 3/75:30 am
ORD
-
ONT
2 stops20h 29m
Frontier
Deal found 1/27$158
This CheapOair deal was found by Cheapflights users on 1/28. 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 1/28$169
This Kiwi.com deal was found by Cheapflights users on 1/28. 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 3/38:40 am
ONT
-
ORD
2 stops24h 11m
Frontier
Thu 3/54:16 pm
ORD
-
ONT
1 stop9h 43m
Frontier
Deal found 1/28$170
This Kiwi.com deal was found by Cheapflights users on 1/27. 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 3/242:23 pm
ONT
-
ORD
1 stop13h 45m
Frontier
Wed 4/15:15 pm
ORD
-
ONT
1 stop27h 30m
Frontier
Deal found 1/27$172
This Mytrip deal was found by Cheapflights users on 1/27. 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.
Thu 2/262:08 pm
ONT
-
ORD
1 stop7h 06m
Frontier
Mon 3/27:19 pm
ORD
-
ONT
1 stop19h 52m
Frontier
Deal found 1/27$174
This CheapOair deal was found by Cheapflights users on 1/28. 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 2/193:24 pm
ONT
-
STL
1 stop28h 02m
Frontier
Mon 2/231:54 pm
STL
-
ONT
1 stop12h 05m
Frontier
Deal found 1/28$179
This Frontier deal was found by Cheapflights users on 1/27. 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 4/147:29 pm
ONT
-
ORD
1 stop9h 18m
Frontier
Sat 4/184:55 pm
ORD
-
ONT
1 stop7h 47m
Frontier
Deal found 1/27$180
This Kiwi.com deal was found by Cheapflights users on 1/26. 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 2/138:07 am
ONT
-
STL
1 stop11h 19m
Frontier
Mon 2/1610:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/26$182
This Kiwi.com deal was found by Cheapflights users on 1/28. 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 3/114:28 pm
ORD
-
ONT
2 stops22h 43m
Frontier
Deal found 1/28$188
This CheapOair deal was found by Cheapflights users on 1/26. 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 4/86:20 am
ONT
-
ORD
1 stop5h 59m
Frontier
Thu 4/1610:55 am
ORD
-
ONT
1 stop15h 00m
Frontier
Deal found 1/26$191

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 29, 2026.

Most accurate provider

FlightHub
3 stars

Most trusted provider

FlightHub
3 stars

Round-trip from

$148
(Frontier)

One-way from

$67
(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. 10% potential increase in price ($34 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 29, 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

Wed 2/25

8:40 am-3:53 pm

1 stop5h 13m

Lambert-St Louis

Sat 2/28

2:51 pm-11:59 pm

1 stop11h 08m

$148

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/19

3:24 pm-9:26 pm

1 stop28h 02m

Lambert-St Louis

Mon 2/23

1:54 pm-11:59 pm

1 stop12h 05m

$179

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/13

2:21 pm-6:51 am

2 stops14h 30m

Lambert-St Louis

Mon 2/16

10:11 pm-1:11 pm

1 stop17h 00m

$230

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/14

6:00 am-1:56 pm

1 stop5h 56m

Lambert-St Louis

Tue 2/24

3:49 pm-6:22 pm

2 stops28h 33m

$239

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 3/1

2:08 pm-1:09 pm

1 stop21h 01m

Lambert-St Louis

Wed 3/4

5:18 pm-9:34 pm

1 stop6h 16m

$260

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 3/24

5:09 pm-12:21 am

1 stop5h 12m

Lambert-St Louis

Wed 3/25

6:00 am-11:47 am

1 stop7h 47m

$277

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/21

6:00 am-1:32 pm

1 stop5h 32m

Lambert-St Louis

Sat 2/28

7:00 am-12:07 pm

1 stop7h 07m

$279

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 3/1

10:20 pm-9:06 am

1 stop8h 46m

Lambert-St Louis

Tue 3/3

7:00 am-12:07 pm

1 stop7h 07m

$285

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/24

5:00 pm-12:25 am

1 stop5h 25m

Lambert-St Louis

Sun 3/1

6:40 pm-11:49 pm

1 stop7h 09m

$285

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/18

10:20 pm-9:06 am

1 stop8h 46m

Lambert-St Louis

Sun 2/22

7:00 am-12:07 pm

1 stop7h 07m

$293

Flights are sorted by cheapest round-trip flights first.

Deals found on 1/27

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 January 29, 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 29, 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
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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
4,267 reviews
Southwest
8.0
Very good
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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
8,128 reviews
Southwest
8.0
Very good
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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
9,215 reviews
Southwest
8.0
Very good
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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
11,205 reviews
Southwest
8.0
Very good
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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
3,056 reviews
Southwest
8.0
Very good
4,267 reviews

Overall

8.0

Entertainment

7.5

Food

7.0

Crew

8.6

Boarding

8.1

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 $148, Frontier can have you in Illinois from Ontario in 5h 13m. 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?

    $82 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 $627, 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 $173 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 29, 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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