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$65+ Cheap flights from St. Louis to Ontario (STL - ONT)

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 1/12. Fares are subject to change and may not be available on all flights or dates of travel.
STL — ONT
Dec 12 — Dec 191
Fri 12/12
Fri 12/19
1 adult, Economy
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1. Tell us where you want to go

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Cheapflights Tip: The best prices from Lambert-St Louis to Ontario are usually found in February or August, booked 65 days in advance, depart on a Tuesday or Wednesday and return on a Monday

Find flight deals from St. Louis to Ontario

Cheapest flights from St. Louis to Ontario
Explore the most affordable flight options available from St. Louis to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on November 12, 2025.

This CheapOair deal was found by Cheapflights users on 11/11. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 12/510:44 pmSTL - ONT
1 stop24h 33mFrontier
Wed 12/106:15 amONT - STL
1 stop27h 57mFrontier
Deal found 11/11$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.
Sun 12/71:16 pmSTL - ONT
1 stop10h 01mFrontier
Thu 12/116:15 amONT - STL
1 stop27h 57mFrontier
Deal found 11/10$138
This CheapOair deal was found by Cheapflights users on 11/11. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 12/19:54 pmSTL - ONT
1 stop25h 23mFrontier
Sun 12/76:15 amONT - STL
1 stop27h 57mFrontier
Deal found 11/11$141
This CheapOair deal was found by Cheapflights users on 11/12. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 12/81:16 pmSTL - ONT
1 stop10h 01mFrontier
Fri 12/123:20 pmONT - STL
1 stop16h 54mFrontier
Deal found 11/12$142
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.
Tue 11/259:54 pmSTL - ONT
1 stop25h 12mFrontier
Sun 11/3012:58 amONT - STL
1 stop7h 04mFrontier
Deal found 11/10$144
This Trip.com deal was found by Cheapflights users on 11/11. 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 Trip.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 11/249:54 pmSTL - ONT
1 stop18h 32mFrontier
Thu 11/2712:58 amONT - STL
1 stop7h 04mFrontier
Deal found 11/11$146
This Booking.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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 11/239:54 pmSTL - ONT
1 stop25h 12mFrontier
Thu 11/2712:58 amONT - STL
1 stop7h 04mFrontier
Deal found 11/9$147
This Booking.com deal was found by Cheapflights users on 11/12. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 12/137:43 pmSTL - ONT
1 stop21h 23mFrontier
Sun 12/145:18 pmONT - STL
1 stop16h 54mFrontier
Deal found 11/12$151
This Mytrip deal was found by Cheapflights users on 11/12. 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 Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 12/2910:10 pmSTL - ONT
1 stop21h 12mFrontier
Thu 1/16:45 amONT - STL
1 stop25h 17mFrontier
Deal found 11/12$156
This Kiwi.com deal was found by Cheapflights users on 11/12. 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 Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 11/259:54 pmSTL - ONT
1 stop25h 12mFrontier
Tue 12/26:15 amONT - STL
2 stops25h 59mFrontier
Deal found 11/12$171
This CheapOair deal was found by Cheapflights users on 11/11. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 12/41:16 pmSTL - ONT
1 stop25h 54mFrontier
Thu 12/112:59 pmONT - STL
1 stop19h 13mFrontier
Deal found 11/11$176

Cheap flight deals from St. Louis to Ontario

Discover tips and strategies to find the most affordable flight options for your journey from St. Louis (STL) to Ontario (ONT). 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 12, 2025.

Most accurate provider

Mytrip
3 stars

Most trusted provider

Mytrip
3 stars

Round-trip from

$130
(CheapOair)

One-way from

$65
(Frontier)

Popular in

March

Cheapest in

February

Average price

$332
Provider with most accurate pricing for Lambert-St Louis-Ontario flight deals.
Search Deals
Provider most trusted by Cheapflights users for Lambert-St Louis-Ontario flights.
Search Deals
From Lambert-St Louis to Ontario
Search Deals
One-way flight from Lambert-St Louis to Ontario
Search Deals
Highest demand for flights based on searches. 9% potential increase in price ($36 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 8% potential price decrease ($28 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in November 2025
Search Deals

Cheapflights Fare Finder

 
Customize your flight search to find flights from St. Louis to Ontario 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 12, 2025.
Use the filters below to find and compare flights from St. Louis to Ontario that are best for you.

Fly from

St. Louis

Fly to

Ontario

Route

Depart

Return

Price

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Mon 11/17

9:07 pm-8:42 pm

1 stop25h 35m

Ontario

Sun 11/23

12:58 am-10:02 am

1 stop7h 04m

$183

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 11/22

7:43 pm-11:28 am

1 stop17h 45m

Ontario

Fri 11/28

7:48 pm-10:02 am

1 stop12h 14m

$218

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 11/22

7:43 pm-11:57 pm

1 stop6h 14m

Ontario

Mon 11/24

5:06 pm-9:09 pm

1 stop26h 03m

$218

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 12/19

7:43 pm-11:59 pm

1 stop6h 16m

Ontario

Sat 12/27

6:00 am-9:25 pm

1 stop13h 25m

$218

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sun 12/7

1:16 pm-9:17 pm

1 stop10h 01m

Ontario

Sun 12/14

5:18 pm-12:12 pm

1 stop16h 54m

$219

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 1/16

9:47 pm-2:33 pm

1 stop18h 46m

Ontario

Sun 1/25

6:00 am-10:02 am

1 stop26h 02m

$277

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 12/23

10:10 pm-9:17 pm

1 stop25h 07m

Ontario

Thu 1/1

6:45 am-10:02 am

1 stop25h 17m

$292

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 12/5

8:05 pm-11:58 pm

1 stop5h 53m

Ontario

Sun 12/7

12:12 pm-11:42 pm

1 stop9h 30m

$293

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 12/2

6:30 am-12:34 pm

1 stop8h 04m

Ontario

Sun 12/7

12:12 pm-11:42 pm

1 stop9h 30m

$293

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 1/31

7:43 pm-11:59 pm

1 stop6h 16m

$65

Flights are sorted by cheapest round-trip flights first.

Deals found on 11/11

Showing 1-10 of 21 results
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Compare providers for flights from St. Louis to Ontario

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 St. Louis to Ontario 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
CheapfaremartPrice Accuracy-Trust Score*1 star
JustAirTicketPrice Accuracy-Trust Score*1 star
MytripPrice Accuracy3 starsTrust Score*3 stars
CheapflightsfaresPrice Accuracy3 starsTrust Score*2 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 St. Louis-Ontario flights, users find the pricing of Mytrip to be most consistent on Cheapflights vs. Mytrip Users can find the same prices on St. Louis-Ontario flight deals on Cheapflights vs. Mytrip >95% of the time. Price accuracy is based on data collected from St. Louis-Ontario flight searches over the past month and is updated monthly.
  • Most trusted provider: When it comes to deals on St. Louis-Ontario flights, Cheapflights users trust Mytrip the most. Mytrip 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 St. Louis-Ontario 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 St. Louis to Ontario

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

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

Use this chart to determine the optimal time to book a round-trip flight from St. Louis to Ontario. Price data was last updated on November 7, 2025.

The price you pay for your flight from St. Louis to Ontario may vary depending on when you book. For the best chance of a lower fare, look to book 65 days in advance of your trip. Fares are likely to increase a fortnight or so before your departure date.

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

Currently, November is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $67). Flying from St. Louis to Ontario in June is currently the most expensive (average of $248). 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 STL to ONT?

Find hourly flight availability from St. Louis to Ontario. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated November 12, 2025.

It’s optimal to fly from St. Louis to Ontario in the evening. By choosing this option you can save up to 71% on the cost of your flight, compared to a flight in the morning.

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

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

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

Reviews of airlines servicing Ontario

Get insights into the airlines that provide service to Ontario. 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 Ontario. Reviews last updated November 12, 2025.
Peruse reviews from past customers who have flown with Southwest, Delta, and United Airlines from St. Louis to Ontario to help guide your decision. 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

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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
8,009 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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
9,015 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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
11,049 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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
3,114 reviews
Southwest
8.0
Very good
4,235 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Overall

8.0

Crew

8.6

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 St. Louis to Ontario. 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 St. Louis to Ontario?

    There are many flights that can get you from St. Louis to Ontario in 25h 35m. Fly via Frontier to get the fastest option. The distance between St. Louis and Ontario is about 1541 mi.

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

    Frontier, at $108, was found to be the cheapest airline from St. Louis to Ontario.Alternate airlines to your destination round-trip include Delta and American Airlines. Frontier is priced at 69% lower than the current average price of a flight leaving 3 months from now.

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

    The cheapest airline one-way is Frontier, with whom users have recently found tickets for as low as $65. However, be on the lookout for offers from Delta and Alaska Airlines, as they are both options that can get you from St. Louis to Ontario for a low price.

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

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

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

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

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

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

    Currently, November is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $67). Flying from St. Louis to Ontario in June is currently the most expensive (average of $248). 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 St. Louis to Ontario

See prices for flight routes from nearby airports that may be better suited for you.
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Top 5 airlines flying from St. Louis to Ontario

Discover the top 5 airlines that operate flights from St. Louis to Ontario. 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 12, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$108Average$242FlexibilityNo cancel feeOn-time62%
DeltaCheapest$171Average$362FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$264Average$356FlexibilityNo cancel feeOn-time71%
SouthwestCheapest$292Average$400FlexibilityNo cancel feeOn-time63%
United AirlinesCheapest$292Average$425FlexibilityNo cancel feeOn-time69%

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