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$63+ 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 1/6. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Dec 20 — Dec 271
Sat 12/20
Sat 12/27
1 adult, Economy
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1. Tell us where you want to go

Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”

2. Select your favorite providers

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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 November 20, 2025.

Most accurate provider

CheapOair
3 stars

Most trusted provider

CheapOair
3 stars

Round-trip from

$138
(Frontier)

One-way from

$63
(Trip.com)

Popular in

March

Cheapest in

January

Average price

$296
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.
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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. 16% potential increase in price ($67 potential increase over avg. RT price).
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Cheapest flight prices on average. 3% potential price decrease ($12 potential savings vs. average RT price).
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Average for round-trip flights in November 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 November 20, 2025.

This CheapOair deal was found by Cheapflights users on 11/19. 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 12/36:15 amONT - STL
1 stop27h 57mFrontier
Fri 12/510:44 pmSTL - ONT
1 stop24h 33mFrontier
Deal found 11/19$146
This Booking.com deal was found by Cheapflights users on 11/19. 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 12/296:00 amONT - STL
1 stop13h 25mFrontier
Wed 1/143:43 pmSTL - ONT
1 stop9h 16mFrontier
Deal found 11/19$151
This Booking.com deal was found by Cheapflights users on 11/19. 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.
Thu 12/116:15 amONT - STL
1 stop27h 57mFrontier
Sat 12/137:43 pmSTL - ONT
1 stop21h 23mFrontier
Deal found 11/19$155
This Mytrip deal was found by Cheapflights users on 11/19. 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.
Wed 12/246:00 pmONT - STL
1 stop20h 24mFrontier
Fri 1/210:10 pmSTL - ONT
1 stop27h 11mFrontier
Deal found 11/19$183
This Kiwi.com deal was found by Cheapflights users on 11/20. 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.
Wed 12/106:15 amONT - STL
1 stop27h 57mFrontier
Fri 12/127:43 pmSTL - ONT
1 stop20h 42mFrontier
Deal found 11/20$200
This CheapOair deal was found by Cheapflights users on 11/20. 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 12/46:15 amONT - STL
1 stop27h 57mFrontier
Fri 12/510:44 pmSTL - ONT
1 stop24h 33mFrontier
Deal found 11/20$217
This Booking.com deal was found by Cheapflights users on 11/19. 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.
Sat 12/205:16 pmONT - STL
1 stop26h 09mFrontier
Sun 12/2810:10 pmSTL - ONT
1 stop25h 07mFrontier
Deal found 11/19$218
This CheapOair deal was found by Cheapflights users on 11/19. 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.
Sun 12/216:00 amONT - STL
1 stop13h 25mFrontier
Mon 12/2910:10 pmSTL - ONT
1 stop25h 07mFrontier
Deal found 11/19$224
This CheapOair deal was found by Cheapflights users on 11/20. 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.
Mon 12/226:00 pmONT - STL
1 stop25h 25mFrontier
Mon 1/510:10 pmSTL - ONT
1 stop18h 59mFrontier
Deal found 11/20$233
This Booking.com deal was found by Cheapflights users on 11/19. 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 12/246:00 pmONT - STL
1 stop20h 24mFrontier
Wed 12/315:19 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 11/19$243

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 November 20, 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

Wed 12/24

6:00 pm-4:24 pm

1 stop20h 24m

Lambert-St Louis

Fri 1/2

10:10 pm-11:21 pm

1 stop27h 11m

$183

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 12/4

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Fri 12/5

10:44 pm-9:17 pm

1 stop24h 33m

$217

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/20

5:16 pm-9:25 pm

1 stop26h 09m

Lambert-St Louis

Sun 12/28

10:10 pm-9:17 pm

1 stop25h 07m

$218

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/26

6:00 am-9:25 pm

1 stop13h 25m

Lambert-St Louis

Mon 12/29

10:10 pm-5:22 pm

1 stop21h 12m

$224

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/6

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Mon 12/8

1:16 pm-9:17 pm

1 stop10h 01m

$253

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/27

6:00 am-9:25 pm

1 stop13h 25m

Lambert-St Louis

Tue 12/30

10:10 pm-5:15 pm

1 stop21h 05m

$289

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 12/24

6:00 pm-4:24 pm

1 stop20h 24m

Lambert-St Louis

Tue 12/30

10:10 pm-5:15 pm

1 stop21h 05m

$289

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 1/2

6:45 am-10:02 am

1 stop25h 17m

Lambert-St Louis

Sun 1/4

10:10 pm-9:17 pm

1 stop25h 07m

$313

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 1/13

12:41 pm-11:39 pm

1 stop8h 58m

Lambert-St Louis

Sat 1/17

7:00 am-12:16 pm

1 stop7h 16m

$323

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 12/1

6:30 am-9:09 pm

1 stop12h 39m

Lambert-St Louis

Wed 12/3

7:43 pm-11:09 am

1 stop17h 26m

$333

Flights are sorted by cheapest round-trip flights first.

Deals found on 11/19

Showing 1-10 of 21 results
1
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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 November.
ProviderPrice AccuracyTrust Score*
ExpediaPrice Accuracy2 starsTrust Score*3 stars
FlightHubPrice Accuracy3 starsTrust Score*1 star
eDreamsPrice Accuracy3 starsTrust Score*3 stars
PricelinePrice Accuracy1 starTrust Score*3 stars
JustAirTicketPrice Accuracy-Trust Score*1 star
CheapOairPrice Accuracy3 starsTrust Score*3 stars
GotogatePrice Accuracy3 starsTrust 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 November 14, 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, 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.

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 November 20, 2025.

A simple way to save on the total cost of your ticket is to fly from Ontario to St. Louis in the evening. If you’re flexible enough to do this you can expect to save up to 59% on your trip compared to booking a flight in the afternoon.

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. Sunday at noon 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 November 20, 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
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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
4,251 reviews
Southwest
8.0
Very good
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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
7.9
Good
8,002 reviews
Southwest
8.0
Very good
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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
9,028 reviews
Southwest
8.0
Very good
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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
11,047 reviews
Southwest
8.0
Very good
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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
3,104 reviews
Southwest
8.0
Very good
4,251 reviews

Overall

8.0

Entertainment

7.5

Boarding

8.1

Crew

8.6

Food

7.0

Comfort

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 $183, Frontier can have you in St. Louis from Ontario in 20h 24m. 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 $130. Additional round-trip tickets that might be worth considering are offered by United Airlines and American Airlines, with the lowest prices starting at $292 and $296, 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, 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
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 November 20, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$130Average$226FlexibilityNo cancel feeOn-time62%
United AirlinesCheapest$292Average$468FlexibilityNo cancel feeOn-time69%
American AirlinesCheapest$296Average$407FlexibilityNo cancel feeOn-time71%
DeltaCheapest$298Average$401FlexibilityNo cancel feeOn-timeN/A
SouthwestCheapest$340Average$421FlexibilityNo cancel feeOn-time63%

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