$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 1/21. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Jan 16 — Jan 231
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 September or November, booked 83 days in advance, depart on a Monday or Tuesday and return on a Tuesday
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 December 17, 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 December 17, 2025.
This Frontier deal was found by Cheapflights users on 12/15. 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 12/246:00 amONT - STL
1 stop8h 24mFrontier
Wed 12/247:43 pmSTL - ONT
1 stop6h 16mFrontier
Deal found 12/15![Frontier logo]()
$228
This CheapOair deal was found by Cheapflights users on 12/15. 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 amONT - STL
1 stop13h 25mFrontier
Mon 1/57:43 pmSTL - ONT
1 stop28h 29mFrontier
Deal found 12/15![Frontier logo]()
$254
This CheapOair deal was found by Cheapflights users on 12/16. 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 12/286:37 pmONT - STL
1 stop24h 48mFrontier
Thu 1/15:19 pmSTL - ONT
1 stop5h 58mFrontier
Deal found 12/16![Frontier logo]()
$259
This CheapOair deal was found by Cheapflights users on 12/17. 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 CheapOair 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
Thu 1/15:19 pmSTL - ONT
1 stop25h 50mFrontier
Deal found 12/17![Frontier logo]()
$275
This CheapOair deal was found by Cheapflights users on 12/16. 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.
Tue 12/236:17 pmONT - STL
1 stop20h 07mFrontier
Sat 1/310:10 pmSTL - ONT
1 stop25h 17mFrontier
Deal found 12/16![Frontier logo]()
$283
This Frontier deal was found by Cheapflights users on 12/15. 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 12/246:00 amONT - STL
1 stop8h 24mFrontier
Mon 1/57:43 pmSTL - ONT
1 stop6h 16mFrontier
Deal found 12/15![Frontier logo]()
$284
This CheapOair deal was found by Cheapflights users on 12/16. 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 12/186:45 amONT - STL
1 stop25h 17mFrontier
Mon 12/2210:10 pmSTL - ONT
1 stop25h 07mFrontier
Deal found 12/16![Frontier logo]()
$305
This Super.com deal was found by Cheapflights users on 12/16. 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 Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 12/226:00 amONT - STL
1 stop13h 25mFrontier
Tue 12/2310:10 pmSTL - ONT
1 stop21h 05mFrontier
Deal found 12/16![Frontier logo]()
$309
This CheapOair deal was found by Cheapflights users on 12/16. 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.
Tue 12/236:00 amONT - STL
1 stop13h 25mFrontier
Sat 12/2710:10 pmSTL - ONT
1 stop25h 17mFrontier
Deal found 12/16![Frontier logo]()
$313
This Flightnetwork deal was found by Cheapflights users on 12/15. 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 Flightnetwork is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/246:00 amONT - STL
1 stop8h 24mFrontier
Sat 1/310:10 pmSTL - ONT
1 stop25h 17mFrontier
Deal found 12/15![Frontier logo]()
$315
This CheapOair deal was found by Cheapflights users on 12/15. 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.
Sat 12/206:00 amONT - STL
1 stop13h 25mFrontier
Sun 12/2110:10 pmSTL - ONT
1 stop25h 07mFrontier
Deal found 12/15![Frontier logo]()
$319
This CheapOair deal was found by Cheapflights users on 12/15. 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 12/186:17 pmONT - STL
1 stop25h 08mFrontier
Sat 12/2010:10 pmSTL - ONT
1 stop21h 32mFrontier
Deal found 12/15![Frontier logo]()
$325
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 December 17, 2025.
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 | $383 |
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 December 17, 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
Thu 1/22
11:04 am-9:06 pm
1 stop8h 02m
Lambert-St Louis
Thu 1/29
10:01 pm-9:23 am
1 stop13h 22m
$163
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Sat 1/24
7:15 am-2:46 pm
1 stop5h 31m
Lambert-St Louis
Mon 1/26
1:40 pm-12:20 am
1 stop12h 40m
$165
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 1/29
11:04 am-9:06 pm
1 stop8h 02m
Lambert-St Louis
Sat 1/31
3:46 pm-11:24 pm
1 stop9h 38m
$165
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 1/28
7:15 am-2:46 pm
1 stop5h 31m
Lambert-St Louis
Sat 1/31
3:46 pm-11:24 pm
1 stop9h 38m
$165
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 1/8
10:18 pm-12:12 pm
1 stop11h 54m
Lambert-St Louis
Mon 1/12
7:43 pm-11:56 pm
1 stop6h 13m
$182
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 2/4
7:15 am-2:46 pm
1 stop5h 31m
Lambert-St Louis
Thu 2/5
10:01 pm-9:23 am
1 stop13h 22m
$183
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 1/1
6:45 am-10:02 am
1 stop25h 17m
Lambert-St Louis
Sun 1/4
10:10 pm-5:15 pm
1 stop21h 05m
$209
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Wed 1/28
7:15 am-2:46 pm
1 stop5h 31m
Lambert-St Louis
Fri 1/30
7:39 pm-12:20 am
1 stop6h 41m
$217
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Thu 1/22
8:48 pm-8:48 pm
1 stop22h 00m
Lambert-St Louis
Sun 1/25
9:27 pm-2:41 pm
1 stop19h 14m
$218
OntarioSt. Louis
ONT - STL
ONTSTL
Ontario
Fri 2/20
7:57 am-9:26 pm
1 stop11h 29m
Lambert-St Louis
Mon 2/23
1:54 pm-11:59 pm
1 stop12h 05m
$218
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 December.
| Provider | Price Accuracy | Trust Score* |
|---|---|---|
| Price Accuracy2 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*1 star | |
| Price Accuracy1 star | Trust Score*3 stars | |
| Price Accuracy- | Trust Score*1 star | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | 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 December 12, 2025.
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 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 December 17, 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.
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 December 17, 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.
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
Reviews
1 / 20
10.0
ExcellentWilliam Drew,Nov 2025
SJC - HNL
Entertainment
7.5
Crew
8.6
Overall
7.9
Boarding
8.1
Food
7.0
Comfort
8.0
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
Fairview Heights
Maryland Heights
Collinsville
Swansea
Eureka
Glencoe
St. Peters
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 December 17, 2025.
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$146 | Average$227 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$286 | Average$401 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$292 | Average$468 | FlexibilityNo cancel fee | On-time69% | |
| Cheapest$292 | Average$405 | FlexibilityNo cancel fee | On-time71% | |
| Cheapest$346 | Average$426 | FlexibilityNo cancel fee | On-time63% |