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St. Louis

$72+ Cheap flights from Ontario to St. Louis (ONT - STL)

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 10/18. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Oct 16 — Oct 231
Thu 10/16
Thu 10/23
1 adult, Economy
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Cheapflights Tip: The best prices from Ontario to Lambert-St Louis are usually found in January or September, booked 54 days in advance, depart on a Monday or Tuesday and return on a Tuesday

Cheap flight deals from Ontario to St. Louis

Discover tips and strategies to find the most affordable flight options for your journey from Ontario (ONT) to St. Louis (STL). Learn about various techniques such as flexible date searches, comparing prices across and setting up price alerts. Use these methods to find the cheapest flights available for your travel needs. Data last updated September 16, 2025.

Round-trip from

$143
(Priceline)

One-way from

$72
(Cheapflightsfares)

Popular in

March

Cheapest in

January

Average price

$295
From Ontario to Lambert-St Louis
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One-way flight from Ontario to Lambert-St Louis
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Highest demand for flights based on searches. 13% potential increase in price ($56 potential increase over avg. RT price).
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Cheapest flight prices on average. 3% potential price decrease ($11 potential savings vs. average RT price).
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Average for round-trip flights in September 2025
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Find flight deals from Ontario to St. Louis

Cheapest flights from Ontario to St. Louis
Explore the most affordable flight options available from Ontario to St. Louis. Find the lowest fares from popular airlines and budget airlines, with prices last updated on September 16, 2025.

This Mytrip deal was found by Cheapflights users on 9/15. 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 10/27:30 pmONT - STL
1 stop23h 10mFrontier
Sun 10/57:55 pmSTL - ONT
1 stop13h 58mFrontier
Deal found 9/15$143
This Frontier deal was found by Cheapflights users on 9/15. 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.
Fri 9/268:59 pmONT - STL
1 stop10h 07mFrontier
Sun 9/2810:39 amSTL - ONT
1 stop6h 45mFrontier
Deal found 9/15$144
This Booking.com deal was found by Cheapflights users on 9/14. 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.
Tue 9/238:59 pmONT - STL
1 stop10h 07mFrontier
Fri 9/269:35 pmSTL - ONT
1 stop17h 08mFrontier
Deal found 9/14$145
This Booking.com deal was found by Cheapflights users on 9/15. 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.
Fri 9/268:59 pmONT - STL
1 stop10h 07mFrontier
Mon 9/299:29 pmSTL - ONT
1 stop26h 27mFrontier
Deal found 9/15$146
This Cheapflightsfares deal was found by Cheapflights users on 9/14. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 11/88:00 amONT - STL
1 stop5h 56mFrontier
Tue 11/117:45 pmSTL - ONT
1 stop6h 05mFrontier
Deal found 9/14$155
This Booking.com deal was found by Cheapflights users on 9/14. 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.
Sun 9/288:59 pmONT - STL
1 stop10h 07mFrontier
Fri 10/37:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 9/14$157
This Frontier deal was found by Cheapflights users on 9/14. 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 10/236:05 amONT - STL
1 stop5h 57mFrontier
Mon 10/2712:38 pmSTL - ONT
1 stop11h 27mFrontier
Deal found 9/14$175
This Booking.com deal was found by Cheapflights users on 9/14. 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.
Mon 10/66:00 amONT - STL
1 stop5h 53mFrontier
Mon 10/137:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/14$176
This Cheapflightsfares deal was found by Cheapflights users on 9/13. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 10/66:00 amONT - STL
1 stop5h 53mFrontier
Wed 10/87:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 9/13$185
This Frontier deal was found by Cheapflights users on 9/14. 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.
Fri 9/198:59 pmONT - STL
1 stop10h 07mFrontier
Thu 9/2510:49 amSTL - ONT
1 stop6h 40mFrontier
Deal found 9/14$188

Cheapflights Fare Finder

 
Customize your flight search to find flights from Ontario to St. Louis 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 September 16, 2025.
Use the filters below to find and compare flights from Ontario to St. Louis that are best for you.

Fly from

Ontario

Fly to

St. Louis

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 10/3

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Tue 10/7

7:52 pm-11:50 pm

1 stop5h 58m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 11/11

6:53 am-9:07 am

1 stop24h 14m

Lambert-St Louis

Fri 11/14

7:45 pm-11:10 am

1 stop17h 25m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 11/13

6:00 am-1:57 pm

1 stop5h 57m

Lambert-St Louis

Mon 11/17

7:45 pm-11:50 pm

1 stop6h 05m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 10/14

7:04 am-9:07 am

1 stop24h 03m

Lambert-St Louis

Tue 10/21

7:52 pm-11:50 pm

1 stop5h 58m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 9/26

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Sun 9/28

10:39 am-3:24 pm

1 stop6h 45m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 10/7

7:04 am-9:07 am

1 stop24h 03m

Lambert-St Louis

Sat 10/11

7:52 pm-11:50 pm

1 stop5h 58m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/9

6:05 am-11:43 am

1 stop27h 38m

Lambert-St Louis

Mon 10/13

7:52 pm-11:50 pm

1 stop5h 58m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/16

10:05 am-11:43 am

1 stop23h 38m

Lambert-St Louis

Tue 10/21

7:52 pm-11:50 pm

1 stop5h 58m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/23

6:05 am-11:43 am

1 stop27h 38m

Lambert-St Louis

Mon 10/27

9:59 pm-8:42 pm

1 stop24h 43m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 9/26

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Mon 9/29

9:29 pm-9:56 pm

1 stop26h 27m

$146

Flights are sorted by cheapest round-trip flights first.

Deals found on 9/16

Showing 1-10 of 24 results
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Best time to book a flight from Ontario to St. Louis

Have a flexible travel schedule? Discover the best time to fly to St. Louis 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 St. Louis

How far ahead should I book a flight from Ontario to St. Louis?

Use this chart to determine the optimal time to book a round-trip flight from Ontario to St. Louis. Price data was last updated on September 12, 2025.

The best time to book flights from Ontario to St. Louis is 54 days before your desired departure date. The cost of your flight will likely increase significantly if you book two weeks in advance of your flight.

What is the cheapest month to book a flight from Ontario to St. Louis?

Currently, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). 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 STL?

Find hourly flight availability from Ontario to St. Louis. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated September 16, 2025.

A simple way to save on the total cost of your ticket is to fly from Ontario to St. Louis in the afternoon. If you’re flexible enough to do this you can expect to save up to 60% on your trip compared to booking a flight at noon.

What is the cheapest day to fly from Ontario to St. Louis?

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

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

Reviews of airlines servicing St. Louis

Get insights into the airlines that provide service to St. Louis. 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 St. Louis. Reviews last updated September 16, 2025.
Get a feel of what it's like to fly with Southwest, Delta, and United Airlines from Ontario to St. Louis by reading reviews from past customers. Users have also rated airlines in terms of entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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
4,242 reviews
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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
8.0
Very good
7,957 reviews
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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
8,924 reviews
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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
10,000 reviews
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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
3,174 reviews
Southwest
8.0
Very good
4,242 reviews

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

8.0

Entertainment

7.5

Overall

8.0

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 St. Louis. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • How long is the flight from Ontario to St. Louis?

    For as low as $143, Frontier can have you in St. Louis from Ontario in 10h 07m. The distance from Ontario to St. Louis is about 1541 mi.

  • What are the cheapest airlines flying from Ontario to St. Louis round-trip?

    Flying on Frontier is currently your cheapest option to St. Louis, with prices starting at $132. Additional round-trip tickets that might be worth considering are offered by Delta and American Airlines, with the lowest prices starting at $298 and $303, respectively. Frontier is priced at 62% lower than the current average price of a flight leaving 3 months from now.

  • Can I find deals for flights from Ontario to St. Louis that include hotel bookings?

    Yes. In addition to deals on Ontario to St. Louis flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Ontario to St. Louis?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Ontario to St. Louis.

  • Can I find deals for business class flights from Ontario to St. Louis?

    Yes. Cheapflights offers flight deals from Ontario to St. Louis 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 St. Louis?

    Currently, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). 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

Traveling to a place near St. Louis?

Book flights to St. Louis if you plan to visit one of these locations
Edwardsville
O'Fallon
Fairview Heights
Maryland Heights
Collinsville
Eureka
Glencoe
St. Peters
Chesterfield
Alton
Farmington
Festus

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Top 5 airlines flying from Ontario to St. Louis

Discover the top 5 airlines that operate flights from Ontario to St. Louis. 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 September 16, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$132Average$228FlexibilityNo cancel feeOn-time62%
DeltaCheapest$298Average$409FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$303Average$415FlexibilityNo cancel feeOn-time71%
United AirlinesCheapest$326Average$506FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$341Average$421FlexibilityNo cancel feeOn-time63%

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