Cheap flights from Ontario to St. Louis from $93

This is the cheapest one-way flight price found by a momondo user in the last 72 hours by searching for a flight from Ontario to St. Louis departing on 8/6. Fares may change, and may not be available for all flights or travel dates. Click the price to refresh the search for this deal.
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0 bags

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Find the cheapest flights from Ontario to St. Louis

Cheap round-trip flights

Southwest Logo
11:15 am - 8:55 pmONT-STL
7h 40m1 stop
Southwest Logo
2:05 pm - 7:35 pmSTL-ONT
7h 30m1 stop
$185Southwest
Find Deal
sáb., sep. 13 - mié., sep. 17
Southwest Logo
1:55 pm - 8:55 pmONT-STL
5h 00m1 stop
Southwest Logo
10:15 am - 5:30 pmSTL-ONT
9h 15m2 stops
$190Southwest
Find Deal
sáb., sep. 13 - mié., sep. 17
Frontier Logo
12:59 am - 9:11 amONT-STL
6h 12m1 stop
Frontier Logo
7:29 pm - 11:50 pmSTL-ONT
6h 21m1 stop
$194Frontier
Find Deal
mar., ago. 12 - sáb., ago. 16
American Airlines Logo
10:20 am - 9:53 pmONT-STL
9h 33m2 stops
American Airlines Logo
5:18 am - 11:56 amSTL-ONT
8h 38m2 stops
$195American Airlines
Find Deal
sáb., sep. 13 - mié., sep. 17
Alaska Airlines Logo
6:00 am - 5:34 pmONT-STL
9h 34m1 stop
Alaska Airlines Logo
3:35 pm - 12:03 amSTL-ONT
10h 28m1 stop
$203Alaska Airlines
Find Deal
jue., sep. 18 - lun., sep. 22
Frontier Logo
12:59 am - 9:11 amONT-STL
6h 12m1 stop
Frontier Logo
7:29 pm - 11:50 pmSTL-ONT
6h 21m1 stop
$204Frontier
Find Deal
jue., ago. 7 - vie., ago. 15
American Airlines Logo
11:59 pm - 9:00 amONT-STL
7h 01m1 stop
American Airlines Logo
3:53 pm - 9:12 pmSTL-ONT
7h 19m1 stop
$211American Airlines
Find Deal
vie., ago. 15 - lun., ago. 18
American Airlines Logo
12:22 pm - 11:14 pmONT-STL
8h 52m2 stops
American Airlines Logo
3:53 pm - 9:12 pmSTL-ONT
7h 19m1 stop
$216American Airlines
Find Deal
vie., ago. 15 - lun., ago. 18
Alaska Airlines Logo
6:00 am - 5:34 pmONT-STL
9h 34m1 stop
Alaska Airlines Logo
6:33 am - 12:37 pmSTL-ONT
8h 04m1 stop
$239Alaska Airlines
Find Deal
sáb., sep. 27 - sáb., oct. 4
Delta Logo
10:00 pm - 8:12 amONT-STL
8h 12m1 stop
Delta Logo
7:35 am - 12:14 pmSTL-ONT
6h 39m1 stop
$277Delta
Find Deal
jue., ago. 14 - dom., ago. 17

Alaska Airlines flights from Ontario to St. Louis

Our best Alaska Airlines deals on Ontario to St. Louis flight tickets
Alaska Airlines
Sep 18
ONT6:00 amOntario
9h 34m
1 stop
STL5:34 pmLambert-St Louis
Sep 22
STL3:35 pmLambert-St Louis
10h 28m
1 stop
ONT12:03 amOntario
Alaska Airlines
Sep 27
ONT6:00 amOntario
9h 34m
1 stop
STL5:34 pmLambert-St Louis
Oct 4
STL6:33 amLambert-St Louis
8h 04m
1 stop
ONT12:37 pmOntario
Alaska Airlines
Jul 22
ONT12:00 pmOntario
9h 59m
1 stop
STL11:59 pmLambert-St Louis
Jul 29
STL3:24 pmLambert-St Louis
10h 51m
1 stop
ONT12:15 amOntario

American Airlines flights from Ontario to St. Louis

Our best American Airlines deals on Ontario to St. Louis flight tickets
American Airlines
Sep 13
ONT10:20 amOntario
9h 33m
2 stops
STL9:53 pmLambert-St Louis
Sep 17
STL5:18 amLambert-St Louis
8h 38m
2 stops
ONT11:56 amOntario
American Airlines
Aug 15
ONT11:59 pmOntario
7h 01m
1 stop
STL9:00 amLambert-St Louis
Aug 18
STL3:53 pmLambert-St Louis
7h 19m
1 stop
ONT9:12 pmOntario
American Airlines
Aug 15
ONT12:22 pmOntario
8h 52m
2 stops
STL11:14 pmLambert-St Louis
Aug 18
STL3:53 pmLambert-St Louis
7h 19m
1 stop
ONT9:12 pmOntario

See travel insights to St. Louis from

How to get the cheapest flight ticket from Ontario to St. Louis

Look no further. We've gone through all the searches for this route on momondo so you have the important information and insights to find the cheapest flight ticket for your trip

What is the typical price of a round-trip flight between Ontario and St. Louis?

What is the cheapest month to fly to St. Louis?

In general, August is the cheapest month to fly from Ontario to St. Louis. Due to it being the ‘off-season’ during this time, you can expect flight prices to be around $221. The month of September is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $267.

What is the cheapest day to depart on your flight to St. Louis?

The cheapest day to depart on your flight to St. Louis is on a Tuesday when prices can be found for as low as $384. This is often the case because there is less demand to fly during this day of the week. If your travel schedule is flexible, try to avoid departing on a Saturday because tickets tend to average around $447. These prices are subject to change though, so be sure to set up a Price Alert for flights to St. Louis.

What is the cheapest time of day to depart on your flight to St. Louis?

Flying to St. Louis from Ontario in the morning is the least expensive time of day to depart. momondo users have found prices as low as $415 when looking at flights departing in the morning. In the afternoon is when there is more demand to fly to St. Louis, so prices are often more expensive at around $426 per ticket.

How far in advance should I book a flight to St. Louis?

You are more likely to see cheaper flights to St. Louis from Ontario when booking weeks ahead of your departure date. In general, you can expect to find flights to St. Louis for around $346 when searching weeks out. However, flight prices might be lower outside of this timeframe. For example, people recently found flights to St. Louis from Ontario for as low as $234 on momondo.

How have Ontario to St. Louis flight prices changed over time?

As of July 2025, prices for Ontario to St. Louis flights are approximately 4% cheaper when compared to flights at the same time last year.

When to book flights from Ontario to St. Louis

Are you open to changing your travel dates? Check out the ideal times to fly from Ontario to St. Louis according to our flight data. Find out which month and days have the cheapest flights.
Estimated round-trip price

Cheap Ontario to St. Louis (ONT to STL) flight deals and tips

Find info about flight duration, direct flights, and airports for your flight from Ontario to St. Louis

Best Price Found

$93

Fastest flight time

5h 00m

Direct flights

None

Airports in St. Louis

1 airport
The best one-way flight to St. Louis from Ontario in the past 72 hours is $93. The best round-trip flight deal from Ontario to St. Louis found on momondo in the last 72 hours is $185.
The fastest flight from Ontario to St. Louis takes 5h 00m
There are no direct flights from Ontario to St. Louis. Popular non-direct route for this connection is Ontario Airport - Lambert-St Louis Airport.
There is 1 airport near St. Louis: Lambert-St Louis (STL)

  • How far is Ontario to Lambert-St Louis by plane?

    There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 00m is a normal flight duration for this route.

  • When did momondo last update prices for flights from Ontario Airport to Lambert-St Louis Airport?

    Prices for flights from Ontario Airport to Lambert-St Louis Airport are updated daily.

  • How many operators does momondo search for flights from Ontario Airport to Lambert-St Louis Airport?

  • How old do you have to be to fly from Ontario Airport to Lambert-St Louis Airport?

    The minimum age for a child to fly alone is five, but airlines that offer an unaccompanied minor (UNMR) service may have their own age limitations. Flight duration, scheduling, and layovers are among the considerations that may influence age limits. We recommend that you double-check with the airline you are booking with for travel from Ontario Airport to Lambert-St Louis Airport.

  • What documentation or ID do you need to fly to Lambert-St Louis Airport?

    The necessary travel and health documents for your Lambert-St Louis Airport trip may vary depending on your travel plans and individual circumstances. Generally, you should have various documents, such as a national ID card or driver's license and a passport that is valid for six months beyond your scheduled arrival date. We recommend seeking advice from your airline or a trusted third party, such as IATA.

  • What is the most popular airline from Ontario to St. Louis?


Best airlines flying from Ontario to St. Louis

Compare and see reviews for airlines that fly from Ontario to St. Louis with momondo
Airline
Rating
Free Cancellation
Price
FrontierPriceFrom $132Free CancellationRating
5.9
3,271 reviews
Search Frontier flights
DeltaPriceFrom $306Free CancellationRating
8.0
7,951 reviews
Search Delta flights
United AirlinesPriceFrom $316Free CancellationRating
7.4
8,846 reviews
Search United Airlines flights
American AirlinesPriceFrom $316Free CancellationRating
7.2
10,000 reviews
Search American Airlines flights
SouthwestPriceFrom $341Free CancellationRating
8.0
4,249 reviews
Search Southwest flights

Traveling to a place near St. Louis?

Book flights to St. Louis if you plan to visit one of these locations
St. Charles
Chesterfield
Hermann
Fairview Heights
Maryland Heights
Florissant
Collinsville
Fenton
Farmington
O'Fallon
St. Peters
Alton
Wentzville
Festus
Glencoe
Clayton
Eureka
Edwardsville
Grafton
Shrewsbury

Why use momondo?

Why should I use momondo to find a flight deal from Ontario to St. Louis?

momondo collates all your flight options in one place and lets you filter them to find the perfect flight from Ontario to St. Louis. momondo saves you time and could save you money on your trip.

Can I find flights from Ontario to St. Louis with flexible booking policies on momondo?

Yes. momondo allows you to filter the results for Ontario to St. Louis flights to just show those with flexible booking policies.

How can momondo help me find flights from Ontario to St. Louis?

Once all potential Ontario to St. Louis flight options are in front of you, momondo lets you sort and filter flights based on preferences such as airline, price and flight times amongst many other options.

I’m not ready to book a flight from Ontario to St. Louis right now. Can momondo alert me if prices change?

If you are not ready to book a flight from Ontario to St. Louis now, use our insights above to find helpful tips or alternatively set up a price alert, where momondo will track prices on flights to St. Louis and let you know when they change.


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1 adult
mar. 7/15
mar. 7/22

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