$74+ 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 2/18. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Feb 25 — Mar 41
1 adult, Economy
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Find cheap flights from Ontario to St. Louis with Cheapflights
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
We find the providers serving your travel needs. Choose up to four travel providers to compare side-by-side for flights, hotels, or car rentals.3. Compare prices and book
Review each provider’s pricing and select the best option for you! Book through your favorite provider’s website for a seamless experience.Cheap flight deals from Ontario to St. Louis
Cheapest flights from Ontario to St. LouisExplore 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 26, 2026.
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 26, 2026.
This Frontier deal was found by Cheapflights users on 1/25. 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.
Wed 2/258:40 am
ONT
- STL
1 stop5h 13m
Frontier
Sat 2/282:51 pm
STL
- ONT
1 stop11h 08m
Frontier
Deal found 1/25![Frontier logo]()
$148
This Kiwi.com deal was found by Cheapflights users on 1/25. 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 2/108:36 am
ONT
- STL
1 stop27h 22m
Frontier
Sat 2/146:41 pm
STL
- ONT
1 stop28h 52m
Frontier
Deal found 1/25![Frontier logo]()
$174
This CheapOair deal was found by Cheapflights users on 1/25. 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 2/187:17 pm
ONT
- STL
1 stop24h 09m
Frontier
Mon 2/2310:11 pm
STL
- ONT
1 stop17h 41m
Frontier
Deal found 1/25![Frontier logo]()
$175
This CheapOair deal was found by Cheapflights users on 1/26. 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 2/193:24 pm
ONT
- STL
1 stop28h 02m
Frontier
Mon 2/231:54 pm
STL
- ONT
1 stop12h 05m
Frontier
Deal found 1/26![Frontier logo]()
$179
This Frontier deal was found by Cheapflights users on 1/25. 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 4/1611:44 am
ONT
- STL
1 stop7h 16m
Frontier
Mon 4/208:12 pm
STL
- ONT
1 stop5h 43m
Frontier
Deal found 1/25![Frontier logo]()
$180
This Mytrip deal was found by Cheapflights users on 1/26. 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.
Sat 2/216:00 am
ONT
- STL
1 stop5h 56m
Frontier
Wed 2/254:51 pm
STL
- ONT
1 stop6h 43m
Frontier
Deal found 1/26![Frontier logo]()
$185
This Mytrip deal was found by Cheapflights users on 1/25. 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 2/43:07 pm
ONT
- STL
1 stop27h 59m
Frontier
Mon 2/99:45 pm
STL
- ONT
1 stop18h 07m
Frontier
Deal found 1/25![Frontier logo]()
$201
This Kiwi.com deal was found by Cheapflights users on 1/26. 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 2/43:07 pm
ONT
- STL
1 stop27h 59m
Frontier
Fri 2/69:43 pm
STL
- ONT
1 stop22h 57m
Frontier
Deal found 1/26![Frontier logo]()
$210
This CheapOair deal was found by Cheapflights users on 1/26. 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 5/75:33 pm
ONT
- STL
1 stop23h 39m
Frontier
Mon 5/118:12 pm
STL
- ONT
1 stop5h 43m
Frontier
Deal found 1/26![Frontier logo]()
$212
This CheapOair deal was found by Cheapflights users on 1/25. 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 2/117:17 pm
ONT
- STL
1 stop24h 09m
Frontier
Mon 2/1610:11 pm
STL
- ONT
1 stop17h 00m
Frontier
Deal found 1/25![Frontier logo]()
$220
This Frontier deal was found by Cheapflights users on 1/25. 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 2/216:00 am
ONT
- STL
1 stop5h 56m
Frontier
Mon 2/231:54 pm
STL
- ONT
1 stop12h 05m
Frontier
Deal found 1/25![Frontier logo]()
$222
Find 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 26, 2026.
Most accurate provider | CheapOair 3 stars |
|---|---|
Most trusted provider | CheapOair 3 stars |
Round-trip from | $148 (Frontier) |
One-way from | $74 (Frontier) |
Popular in | March |
Cheapest in | September |
Average price | $361 |
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 26, 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 2/18
7:30 am-3:53 pm
1 stop6h 23m
Lambert-St Louis
Sat 2/21
2:51 pm-11:59 pm
1 stop11h 08m
$148
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
$148
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 3/4
8:40 am-3:53 pm
1 stop5h 13m
Lambert-St Louis
Tue 3/10
8:06 pm-1:28 pm
1 stop19h 22m
$185
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 2/14
6:00 am-1:56 pm
1 stop5h 56m
Lambert-St Louis
Mon 2/16
1:54 pm-11:59 pm
1 stop12h 05m
$250
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 2/21
7:00 am-3:28 pm
1 stop6h 28m
Lambert-St Louis
Sat 2/28
6:18 pm-10:49 pm
1 stop6h 31m
$260
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sun 3/8
6:15 am-9:49 am
1 stop25h 34m
Lambert-St Louis
Thu 3/12
8:06 pm-8:06 am
1 stop14h 00m
$271
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 4/4
8:19 pm-9:17 pm
1 stop22h 58m
Lambert-St Louis
Sat 4/11
8:16 pm-11:56 pm
1 stop5h 40m
$281
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 2/18
10:20 pm-9:06 am
1 stop8h 46m
Lambert-St Louis
Sun 2/22
6:40 pm-11:49 pm
1 stop7h 09m
$285
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 2/26
12:02 pm-11:59 pm
1 stop9h 57m
Lambert-St Louis
Tue 3/3
7:00 am-3:08 pm
1 stop10h 08m
$293
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 2/19
10:20 pm-9:06 am
1 stop8h 46m
Lambert-St Louis
Sun 2/22
6:40 pm-11:49 pm
1 stop7h 09m
$293
Showing 1-10 of 22 results
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.
| Provider | Price Accuracy | Trust Score* |
|---|---|---|
| Price Accuracy2 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*1 star | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy- | Trust Score*1 star | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy1 star | Trust Score*3 stars |
- 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
Prices
More
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 23, 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.
What’s the top layover airport for flights from Ontario to St. Louis?
Share of 1-stop round-trip flights from Ontario to St. Louis chosen by Cheapflights users in the past 12 months, using the same layover each way.
Las Vegas (LAS) – chosen by Cheapflights users on 71% of 1-stop itineraries from Ontario to St. Louis on Cheapflights.
What’s the cheapest layover airport for flights from Ontario to St. Louis?
Average round-trip fare for 1-stop flights from Ontario to St. Louis, chosen by Cheapflights users in the past 12 months, with the same layover each way.
Las Vegas (LAS) is the most affordable 1-stop option, with an average round-trip price of $328.
What’s the fastest layover option from Ontario to St. Louis?
Shortest average travel time for 1-stop one-way flights from Ontario to St. Louis, based on itineraries clicked by Cheapflights users over the past 12 months, grouped by layover airport.
Flights via Phoenix (PHX) have the shortest average one-way travel time for 1-stop routes: 5h 35m.
Which airport typically offers the quickest layover for flights from Ontario to St. Louis?
Average layover duration for 1-stop one-way flights from Ontario to St. Louis, chosen by Cheapflights users in the last 12 months, grouped by stopover airport.
Flights via Phoenix (PHX) offer the fastest connection on this route, with an average layover time of 1h 09m.
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 26, 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.
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Crew
8.6
Boarding
8.1
Overall
8.0
Comfort
8.0
Food
7.0
Entertainment
7.5
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
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.
Traveling to a place near St. Louis?
Book flights to St. Louis if you plan to visit one of these locationsEdwardsville
O'Fallon
Swansea
Fairview Heights
Maryland Heights
Collinsville
Eureka
Glencoe
Chesterfield
Alton
Farmington
Festus
Browse thousands of different options on Cheapflights for your next trip
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Alternative routes for Ontario to St. Louis
See prices for flight routes from nearby airports that may be better suited for you.
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 26, 2026.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$131 | Average$225 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$139 | Average$401 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$292 | Average$468 | FlexibilityNo cancel fee | On-time69% | |
| Cheapest$292 | Average$413 | FlexibilityNo cancel fee | On-time71% | |
| Cheapest$346 | Average$426 | FlexibilityNo cancel fee | On-time63% |