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$72+ 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 11/5. Fares are subject to change and may not be available on all flights or dates of travel.
STL — ONT
Oct 14 — Oct 211
Tue 10/14
Tue 10/21
1 adult, Economy
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Cheapflights Tip: The best prices from Lambert-St Louis to Ontario are usually found in February or August, booked 77 days in advance, depart on a Tuesday or Wednesday and return on a Monday

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 September 14, 2025.

Round-trip from

$143
(Cheapflightsfares)

One-way from

$72
(Cheapflightsfares)

Popular in

March

Cheapest in

February

Average price

$487
From Lambert-St Louis to Ontario
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One-way flight from Lambert-St Louis to Ontario
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Highest demand for flights based on searches. 5% potential increase in price ($19 potential increase over avg. RT price).
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Cheapest flight prices on average. 5% potential price decrease ($19 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 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 September 14, 2025.

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.
Sat 10/117:52 pmSTL - ONT
1 stop5h 58mFrontier
Sat 10/188:00 amONT - STL
1 stop5h 56mFrontier
Deal found 9/13$143
This Booking.com deal was found by Cheapflights users on 9/12. 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 10/117:52 pmSTL - ONT
1 stop5h 58mFrontier
Tue 10/217:04 amONT - STL
1 stop24h 03mFrontier
Deal found 9/12$144
This Booking.com deal was found by Cheapflights users on 9/11. 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 Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 10/109:59 pmSTL - ONT
1 stop16h 38mFrontier
Sat 10/188:00 amONT - STL
1 stop5h 56mFrontier
Deal found 9/11$145
This Frontier deal was found by Cheapflights users on 9/12. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/2510:49 amSTL - ONT
1 stop6h 40mFrontier
Sun 11/167:22 amONT - STL
1 stop8h 00mFrontier
Deal found 9/12$154
This Mytrip deal was found by Cheapflights users on 9/12. 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.
Fri 10/179:59 pmSTL - ONT
1 stop24h 43mFrontier
Mon 10/206:53 amONT - STL
1 stop24h 14mFrontier
Deal found 9/12$155
This Priceline 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 Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 9/262:38 pmSTL - ONT
1 stop9h 17mFrontier
Sun 9/288:59 pmONT - STL
1 stop10h 07mFrontier
Deal found 9/13$156
This Booking.com deal was found by Cheapflights users on 9/12. 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.
Fri 10/37:55 pmSTL - ONT
1 stop25h 59mFrontier
Mon 10/66:00 amONT - STL
1 stop5h 53mFrontier
Deal found 9/12$157
This Booking.com deal was found by Cheapflights users on 9/12. 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.
Thu 10/910:17 amSTL - ONT
1 stop7h 15mFrontier
Sun 10/1210:47 pmONT - STL
1 stop20h 17mFrontier
Deal found 9/12$158
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.
Thu 10/210:49 amSTL - ONT
1 stop6h 50mFrontier
Mon 10/66:00 amONT - STL
1 stop5h 53mFrontier
Deal found 9/13$174
This Frontier deal was found by Cheapflights users on 9/12. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 10/1610:17 amSTL - ONT
1 stop7h 15mFrontier
Sun 10/1910:47 pmONT - STL
1 stop10h 56mFrontier
Deal found 9/12$175
This Booking.com deal was found by Cheapflights users on 9/12. 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.
Thu 10/1610:17 amSTL - ONT
1 stop7h 15mFrontier
Mon 10/206:53 amONT - STL
1 stop24h 14mFrontier
Deal found 9/12$176
This Frontier deal was found by Cheapflights users on 9/12. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 9/2510:49 amSTL - ONT
1 stop6h 40mFrontier
Mon 11/176:00 amONT - STL
1 stop5h 57mFrontier
Deal found 9/12$185

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 September 14, 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

Thu 9/25

10:49 am-3:29 pm

1 stop6h 40m

Ontario

Sun 10/5

8:59 pm-9:06 am

1 stop10h 07m

$143

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Mon 10/13

9:59 pm-8:42 pm

1 stop24h 43m

Ontario

Sun 10/19

6:44 pm-11:43 am

1 stop14h 59m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Wed 10/22

7:52 pm-11:50 pm

1 stop5h 58m

Ontario

Mon 10/27

6:53 am-9:07 am

1 stop24h 14m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 10/3

7:55 pm-7:54 pm

1 stop25h 59m

Ontario

Tue 10/7

7:04 am-9:07 am

1 stop24h 03m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 9/20

4:58 pm-9:56 pm

1 stop6h 58m

Ontario

Tue 9/23

8:59 pm-9:06 am

1 stop10h 07m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 9/26

2:38 pm-9:55 pm

1 stop9h 17m

Ontario

Sun 9/28

8:59 pm-9:06 am

1 stop10h 07m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 11/1

8:40 pm-12:10 pm

1 stop17h 30m

Ontario

Wed 11/5

6:53 am-9:07 am

1 stop24h 14m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 10/11

7:52 pm-11:50 pm

1 stop5h 58m

Ontario

Sat 10/18

8:00 am-3:56 pm

1 stop5h 56m

$144

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Thu 10/9

10:17 am-3:32 pm

1 stop7h 15m

Ontario

Thu 10/16

10:05 am-11:43 am

1 stop23h 38m

$145

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Fri 10/10

9:59 pm-12:37 pm

1 stop16h 38m

Ontario

Fri 10/17

10:47 pm-3:56 pm

1 stop15h 09m

$145

Flights are sorted by cheapest round-trip flights first.

Deals found on 9/13

Showing 1-10 of 24 results
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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 September 12, 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 66 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, August is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $246). Flying from St. Louis to Ontario in March is currently the most expensive (average of $328). 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 September 14, 2025.

It’s optimal to fly from St. Louis to Ontario in the afternoon. By choosing this option you can save up to 19% 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 Monday evenings when fares are most often at their lowest. Sunday 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 September 14, 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
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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
4,245 reviews
Southwest
8.0
Very good
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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
7,956 reviews
Southwest
8.0
Very good
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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
8,931 reviews
Southwest
8.0
Very good
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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
3,173 reviews
Southwest
8.0
Very good
4,245 reviews

Food

7.0

Comfort

8.0

Crew

8.6

Overall

8.0

Entertainment

7.5

Boarding

8.1

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 6h 40m. 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 $128, 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 65% lower than the current average price of a flight leaving 3 months from now.

  • 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, August is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $246). Flying from St. Louis to Ontario in March is currently the most expensive (average of $328). 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 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 September 14, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$128Average$257FlexibilityNo cancel feeOn-time62%
DeltaCheapest$181Average$362FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$264Average$360FlexibilityNo cancel feeOn-time71%
SouthwestCheapest$336Average$417FlexibilityNo cancel feeOn-time63%
United AirlinesCheapest$344Average$416FlexibilityNo cancel feeOn-time69%

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