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$60+ 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 3/10. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Feb 14 — Feb 211
Sat 2/14
Sat 2/21
1 adult, Economy
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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 January 15, 2026.

Most accurate provider

CheapOair
3 stars

Most trusted provider

CheapOair
3 stars

Round-trip from

$138
(Kiwi.com)

One-way from

$60
(Trip.com)

Popular in

March

Cheapest in

September

Average price

$361
Provider with most accurate pricing for Ontario-Lambert-St Louis flight deals.
Search Deals
Provider most trusted by Cheapflights users for Ontario-Lambert-St Louis flights.
Search Deals
From Ontario to Lambert-St Louis
Search Deals
One-way flight from Ontario to Lambert-St Louis
Search Deals
Highest demand for flights based on searches. 11% potential increase in price ($47 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($9 potential savings vs. average RT price).
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Average for round-trip flights in January 2026
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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 January 15, 2026.

This Kiwi.com deal was found by Cheapflights users on 1/14. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 2/197:22 pm
ONT
-
STL
1 stop24h 04m
Frontier
Mon 2/2310:11 pm
STL
-
ONT
1 stop17h 41m
Frontier
Deal found 1/14$138
This Kiwi.com deal was found by Cheapflights users on 1/14. 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 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
Sat 2/282:51 pm
STL
-
ONT
1 stop19h 08m
Frontier
Deal found 1/14$149
This Trip.com deal was found by Cheapflights users on 1/14. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 2/253:22 pm
ONT
-
STL
1 stop28h 04m
Frontier
Mon 3/210:11 pm
STL
-
ONT
1 stop17h 00m
Frontier
Deal found 1/14$151
This Kiwi.com deal was found by Cheapflights users on 1/13. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 2/262:08 pm
ONT
-
STL
1 stop21h 01m
Frontier
Sat 2/282:51 pm
STL
-
ONT
1 stop19h 08m
Frontier
Deal found 1/13$152
This Frontier deal was found by Cheapflights users on 1/13. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 2/146:00 am
ONT
-
STL
1 stop5h 56m
Frontier
Sat 2/212:51 pm
STL
-
ONT
1 stop11h 08m
Frontier
Deal found 1/13$164
This Booking.com deal was found by Cheapflights users on 1/15. 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.
Wed 2/187:17 pm
ONT
-
STL
1 stop24h 09m
Frontier
Sat 2/282:51 pm
STL
-
ONT
1 stop19h 08m
Frontier
Deal found 1/15$175
This Frontier deal was found by Cheapflights users on 1/15. 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.
Thu 2/511:04 am
ONT
-
STL
1 stop8h 02m
Frontier
Sat 2/73:46 pm
STL
-
ONT
1 stop9h 38m
Frontier
Deal found 1/15$180

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 January 15, 2026.
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

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

$164

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/5

11:04 am-9:06 pm

1 stop8h 02m

Lambert-St Louis

Mon 2/9

1:40 pm-12:20 am

1 stop12h 40m

$180

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/27

2:21 pm-6:51 am

2 stops14h 30m

Lambert-St Louis

Sat 2/28

2:51 pm-7:59 am

1 stop19h 08m

$203

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/21

6:00 am-1:56 pm

1 stop5h 56m

Lambert-St Louis

Fri 2/27

1:59 pm-11:59 pm

1 stop12h 00m

$215

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/28

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sun 2/1

9:32 pm-7:10 pm

1 stop23h 38m

$216

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/6

6:20 am-6:44 pm

1 stop10h 24m

Lambert-St Louis

Sun 2/8

12:03 pm-12:20 am

1 stop14h 17m

$251

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/10

5:05 am-1:16 pm

1 stop6h 11m

Lambert-St Louis

Tue 2/17

4:30 pm-8:50 pm

1 stop6h 20m

$257

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 3/30

9:49 pm-11:19 am

1 stop11h 30m

Lambert-St Louis

Mon 4/6

12:22 pm-8:07 pm

1 stop9h 45m

$259

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/14

6:15 am-5:13 pm

2 stops8h 58m

Lambert-St Louis

Tue 2/24

6:18 pm-10:49 pm

1 stop6h 31m

$263

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/7

7:15 am-8:04 am

2 stops22h 49m

Lambert-St Louis

Mon 2/9

9:45 pm-1:52 pm

1 stop18h 07m

$270

Flights are sorted by cheapest round-trip flights first.

Deals found on 1/14

Showing 1-10 of 20 results
1
2

Compare providers for flights from Ontario to St. Louis

Provider information is updated monthly. Please note that these providers often have deals for this flight, but the availability may vary on a day-by-day basis on Cheapflights.
Use the table below to compare price accuracy, trust ratings, and cancellation policies for each provider offering flight deals from Ontario to St. Louis in January.
ProviderPrice AccuracyTrust Score*
ExpediaPrice Accuracy2 starsTrust Score*3 stars
FlightHubPrice Accuracy3 starsTrust Score*1 star
eDreamsPrice Accuracy3 starsTrust Score*3 stars
JustAirTicketPrice Accuracy-Trust Score*1 star
CheapOairPrice Accuracy3 starsTrust Score*3 stars
GotogatePrice Accuracy3 starsTrust Score*3 stars
PricelinePrice Accuracy1 starTrust Score*3 stars

*The Trust Score is based on feedback from users after their booking experience. It measures overall satisfaction, helping us identify issues like hidden fees, problems during the ticketing process, and the quality of customer service. This score is our best indicator of the provider's quality and reliability.

  • Most accurate provider: When it comes to deals on Ontario-St. Louis flights, users find the pricing of CheapOair to be most consistent on Cheapflights vs. CheapOair Users can find the same prices on Ontario-St. Louis flight deals on Cheapflights vs. CheapOair >95% of the time. Price accuracy is based on data collected from Ontario-St. Louis flight searches over the past month and is updated monthly.
  • Most trusted provider: When it comes to deals on Ontario-St. Louis flights, Cheapflights users trust CheapOair the most. CheapOair has received a user feedback score of 3 out of 3 stars (3 being the best), meaning they have been trusted the most by Cheapflights users looking for Ontario-St. Louis flight deals. Provider user feedback score is based on Cheapflights searches over the past month and is updated monthly.

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 January 9, 2026.

The best time to book flights from Ontario to St. Louis is 82 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, September is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $71). Flying from Ontario to St. Louis in March is currently the most expensive (average of $220). 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.

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 January 15, 2026.
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
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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
4,258 reviews
Southwest
8.0
Very good
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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
8,051 reviews
Southwest
8.0
Very good
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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
9,164 reviews
Southwest
8.0
Very good
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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
11,136 reviews
Southwest
8.0
Very good
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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
4,258 reviews

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

Comfort

8.0

Entertainment

7.5

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 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 $164, Frontier can have you in St. Louis from Ontario in 5h 13m. 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 $131. Additional round-trip tickets that might be worth considering are offered by Delta and United Airlines, with the lowest prices starting at $139 and $292, respectively. Frontier is priced at 63% lower than the current average price of a flight leaving 3 months from now.

  • What are the cheapest airlines to fly from Ontario to St. Louis one-way?

    The cheapest airlines for a one-way flight from Ontario to St. Louis are Frontier ($76), Delta ($140), and Southwest ($165).

  • 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, September is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $71). Flying from Ontario to St. Louis in March is currently the most expensive (average of $220). 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
Swansea
Fairview Heights
Maryland Heights
Collinsville
Eureka
Glencoe
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 January 15, 2026.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$131Average$225FlexibilityNo cancel feeOn-time62%
DeltaCheapest$139Average$401FlexibilityNo cancel feeOn-timeN/A
United AirlinesCheapest$292Average$468FlexibilityNo cancel feeOn-time69%
American AirlinesCheapest$292Average$402FlexibilityNo cancel feeOn-time71%
SouthwestCheapest$346Average$426FlexibilityNo cancel feeOn-time63%

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