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$107+ 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 9/2. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — ORD
Jun 17 — Jun 241
Tue 6/17
Tue 6/24
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 June 12, 2025.

Round-trip from

$234
(CheapOair)

One-way from

$107
(Trip.com)

Popular in

December

Cheapest in

February

Average price

$319

Good round-trip deal

$344 or less

Good one-way deal

$179 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. 7% potential increase in price ($23 potential increase over avg. RT price).
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Cheapest flight prices on average. 1% potential price decrease ($4 potential savings vs. average RT price).
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Average for round-trip flights in June 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 June 12, 2025.

This CheapOair deal was found by Cheapflights users on 6/10. 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.
Tue 8/2612:59 amONT - STL
1 stop6h 12mFrontier
Sun 8/317:54 pmSTL - ONT
1 stop14h 51mFrontier
Deal found 6/10$234
This FlightHub deal was found by Cheapflights users on 6/10. 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 FlightHub is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 8/229:59 amONT - MDW
1 stop9h 49mFrontier
Mon 8/256:31 pmMDW - ONT
1 stop7h 19mFrontier
Deal found 6/10$244
This FlightHub deal was found by Cheapflights users on 6/10. 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 FlightHub is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 8/2112:59 amONT - ORD
1 stop7h 38mFrontier
Mon 8/2512:31 pmORD - ONT
1 stop8h 03mFrontier
Deal found 6/10$244
This Delta deal was found by Cheapflights users on 6/11. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 6/305:08 pmONT - STL
1 stop5h 35mDelta
Sat 7/56:00 amSTL - ONT
1 stop6h 38mDelta
Deal found 6/11$279
This Alaska Airlines deal was found by Cheapflights users on 6/11. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 8/134:00 pmONT - ORD
1 stop11h 40mAlaska Airlines
Sat 8/166:00 amORD - ONT
1 stop10h 46mAlaska Airlines
Deal found 6/11$283
This American Airlines deal was found by Cheapflights users on 6/11. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 7/316:15 amONT - ORD
1 stop5h 48mAmerican Airlines
Thu 7/315:08 pmORD - ONT
1 stop7h 02mAmerican Airlines
Deal found 6/11$295
This Delta deal was found by Cheapflights users on 6/10. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 10/1412:00 pmONT - MDW
1 stop7h 44mDelta
Tue 10/211:05 pmMDW - ONT
1 stop8h 37mDelta
Deal found 6/10$319
This Hawaiian Airlines deal was found by Cheapflights users on 6/11. 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 Hawaiian Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 9/136:00 amONT - ORD
1 stop8h 49mHawaiian Airlines
Wed 9/248:00 amORD - ONT
1 stop8h 09mHawaiian Airlines
Deal found 6/11$323
This Delta deal was found by Cheapflights users on 6/9. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 10/16:45 amONT - ORD
2 stops13h 08mDelta
Tue 10/78:55 amORD - ONT
2 stops12h 47mDelta
Deal found 6/9$329
This Southwest deal was found by Cheapflights users on 6/9. 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 Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 6/305:25 pmONT - STL
1 stop5h 55mSouthwest
Mon 8/117:15 amSTL - ONT
2 stops7h 25mSouthwest
Deal found 6/9$333
This Alaska Airlines deal was found by Cheapflights users on 6/9. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 7/302:21 pmONT - STL
1 stop7h 38mAlaska Airlines
Wed 9/36:00 amSTL - ONT
1 stop10h 09mAlaska Airlines
Deal found 6/9$337
This American Airlines deal was found by Cheapflights users on 6/12. 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 8/112:59 amONT - STL
1 stop6h 19mAmerican Airlines
Thu 8/145:15 amSTL - ONT
2 stops8h 17mAmerican Airlines
Deal found 6/12$343

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 June 12, 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

Tue 8/26

12:59 am-9:11 am

1 stop6h 12m

Lambert-St Louis

Sun 8/31

7:54 pm-8:45 am

1 stop14h 51m

$234

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Fri 8/22

9:59 am-9:48 pm

1 stop9h 49m

Chicago Midway

Mon 8/25

6:31 pm-11:50 pm

1 stop7h 19m

$244

OntarioChicago

ONT - ORD

ONTORD

Ontario

Thu 8/21

12:59 am-10:37 am

1 stop7h 38m

Chicago O'Hare Intl

Mon 8/25

12:31 pm-6:34 pm

1 stop8h 03m

$244

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 6/30

5:08 pm-12:43 am

1 stop5h 35m

Lambert-St Louis

Sat 7/5

6:00 am-10:38 am

1 stop6h 38m

$279

OntarioChicago

ONT - ORD

ONTORD

Ontario

Wed 8/13

4:00 pm-5:40 am

1 stop11h 40m

Chicago O'Hare Intl

Sat 8/16

6:00 am-2:46 pm

1 stop10h 46m

$283

OntarioChicago

ONT - ORD

ONTORD

Ontario

Thu 7/31

6:15 am-2:03 pm

1 stop5h 48m

Chicago O'Hare Intl

Thu 7/31

5:08 pm-10:10 pm

1 stop7h 02m

$295

OntarioChicago

ONT - MDW

ONTMDW

Ontario

Tue 10/14

12:00 pm-9:44 pm

1 stop7h 44m

Chicago Midway

Tue 10/21

1:05 pm-7:42 pm

1 stop8h 37m

$319

OntarioChicago

ONT - ORD

ONTORD

Ontario

Sat 9/13

6:00 am-4:49 pm

1 stop8h 49m

Chicago O'Hare Intl

Wed 9/24

8:00 am-2:09 pm

1 stop8h 09m

$323

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 6/30

5:25 pm-1:20 am

1 stop5h 55m

Lambert-St Louis

Mon 8/11

7:15 am-12:40 pm

2 stops7h 25m

$333

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 7/30

2:21 pm-11:59 pm

1 stop7h 38m

Lambert-St Louis

Wed 9/3

6:00 am-2:09 pm

1 stop10h 09m

$337

Flights are sorted by cheapest round-trip flights first.

Deals found on 6/10

Showing 1-10 of 54 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 June 12, 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.

Rainfall in Illinois by month

Plan your trip to Illinois by taking into account the average rainfall totals by month.

In terms of precipitation, rainfall in Illinois ranges from 1.7 - 4.9 inches per month. August is typically the wettest month, when rainfall can reach 4.9 in. January is typically the driest time to visit Illinois when rainfall is around 1.7 in.

Temperature in Illinois by month

Plan your trip to Illinois by taking into account the average temperature totals by month.

If weather is an important factor for your trip to Illinois, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 73.4 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 23.0 F).

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 June 12, 2025.
Get a feel of what it's like to fly with Alaska Airlines, Southwest and Delta from Ontario to Illinois by reading reviews from past customers. In addition to providing an overall rating, users have also rated airlines in terms of entertainment options, comfort, food, crew/service, and boarding process.
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Alaska Airlines
8.0
Very good
10,000 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Southwest
8.0
Very good
4,287 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Delta
8.0
Very good
7,950 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Hawaiian Airlines
7.9
Good
2,494 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
United Airlines
7.4
Good
8,790 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Boarding

8.1

Comfort

7.8

Food

7.1

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.

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.

  • What are the cheapest airlines to fly from Ontario to Illinois one-way?

    $107 is the cheapest one-way deal found within the past few days, from Frontier. You may also be able to find cheap deals on Alaska Airlines and Delta, with prices starting from $137 and $138, 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 $924, our data shows the cheapest flight currently is $113. When looking at the most popular route, (Ontario - Chicago O'Hare Intl), you can expect to pay $278 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.

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 6 airlines flying from Ontario to Illinois

Discover the top 6 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 June 12, 2025.
AirlineCheapestAverageFlexibilityOn-time
Spirit AirlinesCheapest$99Average$217FlexibilityNo cancel feeOn-time65%
FrontierCheapest$108Average$198FlexibilityNo cancel feeOn-time62%
DeltaCheapest$173Average$393FlexibilityNo cancel feeOn-timeN/A
United AirlinesCheapest$227Average$484FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$237Average$441FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$238Average$518FlexibilityNo cancel feeOn-time71%

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