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Cheap flights from Ontario to St. Louis from $72

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 10/18. 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

Frontier Logo
7:30 pm - 8:40 pmONT-STL
23h 10m1 stop
Frontier Logo
7:55 pm - 7:53 amSTL-ONT
13h 58m1 stop
$143Frontier
Find Deal
Thu, Oct 2 - Sun, Oct 5
Frontier Logo
8:59 pm - 9:06 amONT-STL
10h 07m1 stop
Frontier Logo
10:39 am - 3:24 pmSTL-ONT
6h 45m1 stop
$144Frontier
Find Deal
Fri, Sep 26 - Sun, Sep 28
Frontier Logo
6:54 pm - 9:04 pmONT-STL
24h 10m1 stop
Frontier Logo
7:52 pm - 11:50 pmSTL-ONT
5h 58m1 stop
$145Frontier
Find Deal
Thu, Oct 16 - Tue, Oct 21
Delta Logo
10:00 pm - 9:15 amONT-STL
9h 15m1 stop
Delta Logo
7:30 pm - 11:39 pmSTL-ONT
6h 09m1 stop
$293Delta
Find Deal
Fri, Oct 10 - Mon, Oct 13
American Airlines Logo
4:47 pm - 11:51 pmONT-STL
5h 04m1 stop
American Airlines Logo
9:38 am - 4:03 pmSTL-ONT
8h 25m2 stops
$298American Airlines
Find Deal
Sat, Nov 8 - Tue, Nov 11
American Airlines Logo
12:55 pm - 10:58 pmONT-STL
8h 03m2 stops
American Airlines Logo
7:00 am - 4:03 pmSTL-ONT
11h 03m2 stops
$303American Airlines
Find Deal
Sat, Nov 8 - Tue, Nov 11
Delta Logo
6:00 am - 1:31 pmONT-STL
5h 31m1 stop
Delta Logo
6:50 am - 5:09 pmSTL-ONT
12h 19m2 stops
$359Delta
Find Deal
Sun, Nov 9 - Thu, Nov 13
Southwest Logo
12:45 pm - 9:35 pmONT-STL
6h 50m1 stop
Southwest Logo
5:05 am - 8:50 amSTL-ONT
5h 45m1 stop
$367Southwest
Find Deal
Wed, Dec 24 - Fri, Jan 2
Southwest Logo
11:15 am - 9:00 pmONT-STL
7h 45m1 stop
Southwest Logo
3:45 pm - 10:00 pmSTL-ONT
8h 15m2 stops
$372Southwest
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Wed, Dec 24 - Fri, Jan 2
United Airlines Logo
5:40 am - 4:34 pmONT-STL
8h 54m1 stop
United Airlines Logo
8:30 am - 9:19 pmSTL-ONT
14h 49m1 stop
$391United Airlines
Find Deal
Sat, Feb 21 - Mon, Feb 23

Alaska Airlines flights from Ontario to St. Louis

Our best Alaska Airlines deals on Ontario to St. Louis flight tickets
Alaska Airlines
Oct 15
ONT6:00 amOntario
16h 03m
1 stop
STL12:03 amLambert-St Louis
Oct 22
STL6:33 amLambert-St Louis
8h 04m
1 stop
ONT12:37 pmOntario
$292
Find similar
Alaska Airlines
Nov 20
ONT11:59 amOntario
10h 00m
1 stop
STL11:59 pmLambert-St Louis
Nov 24
STL7:00 amLambert-St Louis
10h 54m
1 stop
ONT3:54 pmOntario
$350
Find similar
Alaska Airlines
Mar 4
ONT11:30 amOntario
10h 26m
1 stop
STL11:56 pmLambert-St Louis
Mar 10
STL2:55 pmLambert-St Louis
9h 42m
1 stop
ONT10:37 pmOntario
$393
Find similar

Delta flights from Ontario to St. Louis

Our best Delta deals on Ontario to St. Louis flight tickets
Delta
Oct 10
ONT10:00 pmOntario
9h 15m
1 stop
STL9:15 amLambert-St Louis
Oct 13
STL7:30 pmLambert-St Louis
6h 09m
1 stop
ONT11:39 pmOntario
$293
Find similar
Delta
Nov 9
ONT6:00 amOntario
5h 31m
1 stop
STL1:31 pmLambert-St Louis
Nov 13
STL6:50 amLambert-St Louis
12h 19m
2 stops
ONT5:09 pmOntario
$359
Find similar
Delta
Mar 1
ONT5:05 pmOntario
5h 32m
1 stop
STL12:37 amLambert-St Louis
Mar 3
STL6:59 pmLambert-St Louis
6h 53m
1 stop
ONT11:52 pmOntario
$384
Find similar

momondo 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, momondo users made 832,500 searches. Data last updated September 16, 2025.
Use the filters below to find and compare flights from Ontario to St. Louis that are best for you.

Fly from

Fly to

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/2

7:30 pm-8:40 pm

1 stop23h 10m

Lambert-St Louis

Sun 10/5

7:55 pm-7:53 am

1 stop13h 58m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 9/26

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Sun 9/28

10:39 am-3:24 pm

1 stop6h 45m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/16

6:54 pm-9:04 pm

1 stop24h 10m

Lambert-St Louis

Tue 10/21

7:52 pm-11:50 pm

1 stop5h 58m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 10/10

10:00 pm-9:15 am

1 stop9h 15m

Lambert-St Louis

Mon 10/13

7:30 pm-11:39 pm

1 stop6h 09m

$293

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/8

4:47 pm-11:51 pm

1 stop5h 04m

Lambert-St Louis

Tue 11/11

9:38 am-4:03 pm

2 stops8h 25m

$298

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/8

12:55 pm-10:58 pm

2 stops8h 03m

Lambert-St Louis

Tue 11/11

7:00 am-4:03 pm

2 stops11h 03m

$303

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 11/9

6:00 am-1:31 pm

1 stop5h 31m

Lambert-St Louis

Thu 11/13

6:50 am-5:09 pm

2 stops12h 19m

$359

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 12/24

12:45 pm-9:35 pm

1 stop6h 50m

Lambert-St Louis

Fri 1/2

5:05 am-8:50 am

1 stop5h 45m

$367

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 12/24

11:15 am-9:00 pm

1 stop7h 45m

Lambert-St Louis

Fri 1/2

3:45 pm-10:00 pm

2 stops8h 15m

$372

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/21

5:40 am-4:34 pm

1 stop8h 54m

Lambert-St Louis

Mon 2/23

8:30 am-9:19 pm

1 stop14h 49m

$391

Flights are sorted by cheapest round-trip flights first.

Showing 1-10 of 20 resultsSorted by cheapest first
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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 cheapest month to fly to St. Louis?

In general, January 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 $212. The month of September is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $295.

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 Thursday when prices can be found for as low as $398. 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 $451. 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 evening is the least expensive time of day to depart. momondo users have found prices as low as $391 when looking at flights departing in the evening. In the afternoon is when there is more demand to fly to St. Louis, so prices are often more expensive at around $430 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 $357 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 $278 on momondo.

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

As of September 2025, prices for Ontario to St. Louis flights are approximately 19% more expensive 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

Direct flights

None
There are no direct flights from Ontario to St. Louis. There are no popular flight routes from Ontario to St. Louis.
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  • How far is Ontario to Lambert-St Louis by plane?

    There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 04m 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
5.8
3,174 reviews
Search Frontier flights
DeltaPriceFrom $298Free CancellationRating
7.9
7,957 reviews
Search Delta flights
American AirlinesPriceFrom $303Free CancellationRating
7.2
10,000 reviews
Search American Airlines flights
United AirlinesPriceFrom $326Free CancellationRating
7.4
8,924 reviews
Search United Airlines flights
SouthwestPriceFrom $341Free CancellationRating
8.0
4,242 reviews
Search Southwest flights

  • Southwest Flights From Ontario to St. Louis

    Southwest operates around 3 flights from Ontario to St. Louis every week. The average price of these flights found in the last 72 hours has been $421, but momondo users have found Southwest deals from Ontario to St. Louis from as low as $341 round-trip. Southwest has been scored 8.0/10 in 4,242 reviews.

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
Florissant
Maryland Heights
O'Fallon
Fenton
Collinsville
Wentzville
Alton
St. Peters
Farmington
Festus
Glencoe
Clayton
Edwardsville
Eureka
Litchfield
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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