$72+ 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 9/3. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Aug 25 — Sep 11
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.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 August 20, 2025.
Round-trip from | $142 (Gotogate) |
|---|---|
One-way from | $72 (Mytrip) |
Popular in | March |
Cheapest in | January |
Average price | $328 |
Find 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 August 20, 2025.
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 August 20, 2025.
This Gotogate deal was found by Cheapflights users on 8/18. 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 Gotogate is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 9/212:59 amONT - STL
1 stop6h 12mFrontier
Sun 9/77:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 8/18![Frontier logo]()
$142
This Mytrip deal was found by Cheapflights users on 8/18. 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.
Tue 9/212:59 amONT - STL
1 stop6h 12mFrontier
Mon 9/87:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 8/18![Frontier logo]()
$143
This Booking.com deal was found by Cheapflights users on 8/18. 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 9/43:43 pmONT - STL
1 stop15h 23mFrontier
Mon 9/87:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 8/18![Frontier logo]()
$144
This Mytrip deal was found by Cheapflights users on 8/18. 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 9/88:59 pmONT - STL
1 stop10h 07mFrontier
Sun 9/1410:39 amSTL - ONT
1 stop9h 36mFrontier
Deal found 8/18![Frontier logo]()
$148
This Booking.com deal was found by Cheapflights users on 8/18. 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 9/128:59 pmONT - STL
1 stop10h 07mFrontier
Sun 9/1410:39 amSTL - ONT
1 stop6h 45mFrontier
Deal found 8/18![Frontier logo]()
$149
This Mytrip deal was found by Cheapflights users on 8/18. 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 9/38:00 amONT - STL
1 stop27h 53mFrontier
Fri 9/57:55 pmSTL - ONT
1 stop25h 59mFrontier
Deal found 8/18![Frontier logo]()
$150
This Booking.com deal was found by Cheapflights users on 8/18. 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 10/34:08 pmONT - STL
1 stop14h 58mFrontier
Mon 10/69:29 pmSTL - ONT
1 stop25h 13mFrontier
Deal found 8/18![Frontier logo]()
$151
This Mytrip deal was found by Cheapflights users on 8/19. 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.
Thu 10/910:05 amONT - STL
1 stop23h 38mFrontier
Sat 10/117:52 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 8/19![Frontier logo]()
$155
This Priceline deal was found by Cheapflights users on 8/18. 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.
Thu 11/67:39 amONT - STL
1 stop7h 48mFrontier
Sun 11/92:42 pmSTL - ONT
1 stop9h 23mFrontier
Deal found 8/18![Frontier logo]()
$156
This Cheapflightsfares deal was found by Cheapflights users on 8/17. 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.
Fri 10/316:00 amONT - STL
1 stop5h 57mFrontier
Sun 11/27:45 pmSTL - ONT
1 stop6h 05mFrontier
Deal found 8/17![Frontier logo]()
$157
This Frontier deal was found by Cheapflights users on 8/17. 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.
Tue 9/212:59 amONT - STL
1 stop6h 12mFrontier
Thu 9/1110:49 amSTL - ONT
1 stop6h 40mFrontier
Deal found 8/17![Frontier logo]()
$158
This Frontier deal was found by Cheapflights users on 8/17. 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.
Fri 9/58:59 pmONT - STL
1 stop10h 07mFrontier
Sat 9/134:58 pmSTL - ONT
1 stop6h 58mFrontier
Deal found 8/17![Frontier logo]()
$160
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 August 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
Tue 9/2
12:59 am-9:11 am
1 stop6h 12m
Lambert-St Louis
Sun 9/7
7:55 pm-7:54 pm
1 stop25h 59m
$142
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Fri 9/12
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Wed 9/17
7:55 pm-7:23 am
1 stop13h 28m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sun 10/12
6:53 am-9:07 am
1 stop24h 14m
Lambert-St Louis
Sat 10/18
7:52 pm-9:35 am
1 stop15h 43m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Tue 9/2
12:59 am-9:11 am
1 stop6h 12m
Lambert-St Louis
Fri 9/5
7:55 pm-7:54 pm
1 stop25h 59m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 9/13
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Mon 9/15
7:55 pm-7:54 pm
1 stop25h 59m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 9/18
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Tue 9/23
7:55 pm-7:54 pm
1 stop25h 59m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Tue 9/16
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Fri 9/19
7:55 pm-7:54 pm
1 stop25h 59m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 9/6
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Wed 9/10
7:55 pm-7:23 am
1 stop13h 28m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Fri 9/26
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Sat 9/27
7:55 pm-7:23 am
1 stop13h 28m
$143
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Tue 9/23
8:59 pm-9:06 am
1 stop10h 07m
Lambert-St Louis
Wed 9/24
7:55 pm-7:23 am
1 stop13h 28m
$143
Showing 1-10 of 23 results
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 August 8, 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, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). 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 August 20, 2025.
A simple way to save on the total cost of your ticket is to fly from Ontario to St. Louis in the afternoon. If you’re flexible enough to do this you can expect to save up to 60% on your trip compared to booking a flight at noon.
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. Monday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.
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 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.
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 August 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.
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
Comfort
8.0
Food
7.0
Crew
8.6
Overall
8.0
Entertainment
7.5
Boarding
8.1
Reviews
1 / 20
8.0
ExcellentWalter,Aug 2025
OAK - SAN
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 locationsO'Fallon
Fairview Heights
Maryland Heights
Collinsville
Eureka
St. Peters
Glencoe
Alton
Chesterfield
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 August 20, 2025.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$131 | Average$226 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$298 | Average$409 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$306 | Average$402 | FlexibilityNo cancel fee | On-time71% | |
| Cheapest$340 | Average$416 | FlexibilityNo cancel fee | On-time63% | |
| Cheapest$346 | Average$506 | FlexibilityNo cancel fee | On-time69% |