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$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 1/27. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
dic. 11 — dic. 181
jue. 12/11
jue. 12/18
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 noviembre 11, 2025.

Most accurate provider

Justfly.com
3 stars

Most trusted provider

Justfly.com
3 stars

Round-trip from

$130
(Expedia)

One-way from

$63
(Trip.com)

Popular in

November

Cheapest in

September

Average price

$338

Good round-trip deal

$336 or less

Good one-way deal

$110 or less
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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 ($31 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 November 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 noviembre 11, 2025.

This Expedia deal was found by Cheapflights users on 11/10. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb. 12/136:15 amONT - STL
1 stop27h 57mFrontier
lun. 12/151:16 pmSTL - ONT
1 stop10h 01mFrontier
Deal found 11/10$130
This CheapOair deal was found by Cheapflights users on 11/10. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
vie. 12/56:15 amONT - STL
1 stop13h 33mFrontier
sáb. 12/67:43 pmSTL - ONT
1 stop21h 23mFrontier
Deal found 11/10$134
This CheapOair deal was found by Cheapflights users on 11/10. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
mié. 11/2612:58 amONT - STL
1 stop16h 00mFrontier
vie. 12/57:43 pmSTL - ONT
1 stop20h 42mFrontier
Deal found 11/10$141
This CheapOair deal was found by Cheapflights users on 11/10. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
vie. 12/56:15 amONT - STL
1 stop13h 33mFrontier
dom. 12/71:16 pmSTL - ONT
1 stop10h 01mFrontier
Deal found 11/10$142
This CheapOair deal was found by Cheapflights users on 11/9. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
mié. 11/265:06 pmONT - STL
1 stop26h 03mFrontier
lun. 12/19:54 pmSTL - ONT
1 stop25h 23mFrontier
Deal found 11/9$144
This Mytrip deal was found by Cheapflights users on 11/9. 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 Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb. 11/227:08 pmONT - STL
1 stop21h 50mFrontier
dom. 11/239:54 pmSTL - ONT
1 stop25h 12mFrontier
Deal found 11/9$146
This Kiwi.com deal was found by Cheapflights users on 11/9. 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.
sáb. 12/133:20 pmONT - MDW
2 stops27h 25mFrontier
dom. 1/187:00 amMDW - ONT
1 stop13h 12mFrontier
Deal found 11/9$166
This CheapOair deal was found by Cheapflights users on 11/10. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb. 12/66:15 amONT - STL
1 stop27h 57mFrontier
lun. 12/81:16 pmSTL - ONT
1 stop10h 01mFrontier
Deal found 11/10$176
This CheapOair deal was found by Cheapflights users on 11/9. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb. 12/63:20 pmONT - MDW
1 stop17h 48mFrontier
jue. 12/118:05 amMDW - ONT
1 stop12h 30mFrontier
Deal found 11/9$176
This Frontier deal was found by Cheapflights users on 11/10. 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.
jue. 12/412:04 pmONT - ORD
1 stop10h 08mFrontier
jue. 12/119:21 amORD - ONT
1 stop11h 14mFrontier
Deal found 11/10$176
This Trip.com deal was found by Cheapflights users on 11/9. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
jue. 11/2012:58 amONT - STL
1 stop7h 04mFrontier
sáb. 11/227:43 pmSTL - ONT
1 stop6h 14mFrontier
Deal found 11/9$180
This Frontier deal was found by Cheapflights users on 11/10. 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.
vie. 12/53:20 pmONT - ORD
1 stop6h 52mFrontier
lun. 12/1512:59 pmORD - ONT
1 stop10h 18mFrontier
Deal found 11/10$180

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 noviembre 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

sáb. 12/13

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

lun. 12/15

1:16 pm-9:17 pm

1 stop10h 01m

$130

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

mar. 1/20

7:00 am-10:02 am

1 stop25h 02m

Lambert-St Louis

vie. 1/23

7:43 pm-11:59 pm

1 stop6h 16m

$134

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

mié. 11/26

12:58 am-6:58 pm

1 stop16h 00m

Lambert-St Louis

dom. 11/30

9:54 pm-9:06 pm

1 stop25h 12m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

lun. 11/24

6:30 am-9:09 pm

1 stop12h 39m

Lambert-St Louis

lun. 12/1

9:54 pm-9:17 pm

1 stop25h 23m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

mié. 11/26

6:30 am-9:09 pm

1 stop12h 39m

Lambert-St Louis

lun. 12/1

9:54 pm-9:17 pm

1 stop25h 23m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

mié. 11/19

12:58 am-6:58 pm

1 stop16h 00m

Lambert-St Louis

mar. 11/25

9:54 pm-2:26 pm

1 stop18h 32m

$183

OntarioChicago

ONT - ORD

ONTORD

Ontario

jue. 11/20

8:45 am-11:56 pm

1 stop13h 11m

Chicago O'Hare Intl

mié. 11/26

6:30 am-4:21 pm

1 stop11h 51m

$183

OntarioChicago

ONT - ORD

ONTORD

Ontario

jue. 1/15

6:56 pm-8:34 am

1 stop11h 38m

Chicago O'Hare Intl

lun. 1/19

9:37 am-6:12 pm

1 stop10h 35m

$196

OntarioChicago

ONT - MDW

ONTMDW

Ontario

jue. 11/20

12:23 pm-6:12 pm

1 stop27h 49m

Chicago Midway

sáb. 11/22

3:55 pm-4:21 pm

1 stop26h 26m

$197

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

lun. 11/24

8:15 am-6:19 pm

1 stop8h 04m

Lambert-St Louis

lun. 11/24

9:54 pm-2:26 pm

1 stop18h 32m

$200

Flights are sorted by cheapest round-trip flights first.

Deals found on 11/9

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 noviembre 11, 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 mornings 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 noviembre 11, 2025.

The most flights from ONT to USIL are scheduled on a Monday (1 on average). You will have fewer flight options on Monday, 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 noviembre 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
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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
4,235 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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
7.9
Good
8,007 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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
9,012 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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
11,045 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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
3,113 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Entertainment

7.5

Overall

8.0

Food

7.0

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 $294, Frontier can have you in Illinois from Ontario in 5h 37m. The distance between Ontario and Illinois is about 1557 mi. Both multi-stop and nonstop flights can be found to your destination and back.

  • 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 $671, our data shows the cheapest flight currently is $183. When looking at the most popular route, (Ontario - Chicago O'Hare Intl), you can expect to pay $130 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.

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Alternative routes for Ontario to Illinois

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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 noviembre 11, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$110Average$217FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$227Average$463FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$237Average$423FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$246Average$490FlexibilityNo cancel feeOn-time71%
DeltaCheapest$256Average$381FlexibilityNo cancel feeOn-timeN/A

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