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Cheap flights from Ontario to St. Louis from $63

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 1/22. 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

Enter your travel dates to find the best prices.
Frontier Logo
8:45 am - 9:07 amONT-STL
22h 22m1 stop
Frontier Logo
9:54 pm - 2:26 pmSTL-ONT
18h 32m1 stop
$130Frontier
Find Deal
Tue, Nov 18 - Thu, Nov 20
Frontier Logo
12:58 am - 6:58 pmONT-STL
16h 00m1 stop
Frontier Logo
9:54 pm - 2:26 pmSTL-ONT
18h 32m1 stop
$131Frontier
Find Deal
Wed, Nov 19 - Thu, Nov 20
Frontier Logo
8:00 am - 3:56 pmONT-STL
5h 56m1 stop
Frontier Logo
7:45 pm - 9:29 pmSTL-ONT
27h 44m1 stop
$150Frontier
Find Deal
Sat, Nov 8 - Tue, Nov 11
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
7:43 pm - 3:06 pmSTL-ONT
21h 23m1 stop
$154Frontier
Find Deal
Fri, Dec 5 - Sat, Dec 6
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
5:44 pm - 2:33 pmSTL-ONT
22h 49m1 stop
$163Frontier
Find Deal
Fri, Dec 12 - Mon, Jan 12
Frontier Logo
6:45 am - 10:02 amONT-STL
25h 17m1 stop
Frontier Logo
5:44 pm - 2:33 pmSTL-ONT
22h 49m1 stop
$172Frontier
Find Deal
Thu, Dec 18 - Mon, Jan 12
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
7:43 pm - 2:33 pmSTL-ONT
44h 50m2 stops
$174Frontier
Find Deal
Fri, Dec 12 - Mon, Jan 12
Frontier Logo
8:00 am - 3:56 pmONT-STL
5h 56m1 stop
Frontier Logo
7:45 pm - 9:29 pmSTL-ONT
27h 44m1 stop
$176Frontier
Find Deal
Sat, Nov 8 - Tue, Nov 11
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
7:43 pm - 11:09 amSTL-ONT
17h 26m1 stop
$177Frontier
Find Deal
Fri, Dec 5 - Wed, Dec 10
Multiple Airlines Logo
6:45 am - 10:02 amONT-STL
25h 17m1 stop
Multiple Airlines Logo
5:06 pm - 2:33 pmSTL-ONT
23h 27m2 stops
$241Multiple Airlines
Find Deal
Thu, Dec 18 - Tue, Jan 13

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Nov 18
ONT8:45 amOntario
22h 22m
1 stop
STL9:07 amLambert-St Louis
Nov 20
STL9:54 pmLambert-St Louis
18h 32m
1 stop
ONT2:26 pmOntario
$130
Find similar
Frontier
Nov 19
ONT12:58 amOntario
16h 00m
1 stop
STL6:58 pmLambert-St Louis
Nov 20
STL9:54 pmLambert-St Louis
18h 32m
1 stop
ONT2:26 pmOntario
$131
Find similar
Frontier
Nov 8
ONT8:00 amOntario
5h 56m
1 stop
STL3:56 pmLambert-St Louis
Nov 11
STL7:45 pmLambert-St Louis
27h 44m
1 stop
ONT9:29 pmOntario
$150
Find similar

American Airlines flights from Ontario to St. Louis

Our best American Airlines deals on Ontario to St. Louis flight tickets
American Airlines
Nov 10
ONT12:55 pmOntario
8h 03m
2 stops
STL10:58 pmLambert-St Louis
Nov 17
STL3:23 pmLambert-St Louis
8h 36m
2 stops
ONT9:59 pmOntario
$528
Find similar
American Airlines
Nov 8
ONT6:11 amOntario
11h 19m
2 stops
STL7:30 pmLambert-St Louis
Nov 11
STL2:29 pmLambert-St Louis
5h 51m
1 stop
ONT6:20 pmOntario
$607
Find similar
American Airlines
Nov 8
ONT6:11 amOntario
11h 19m
2 stops
STL7:30 pmLambert-St Louis
Nov 11
STL9:36 amLambert-St Louis
8h 27m
2 stops
ONT4:03 pmOntario
$612
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 October 28, 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

Tue 11/18

8:45 am-9:07 am

1 stop22h 22m

Lambert-St Louis

Thu 11/20

9:54 pm-2:26 pm

1 stop18h 32m

$130

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 11/19

12:58 am-6:58 pm

1 stop16h 00m

Lambert-St Louis

Thu 11/20

9:54 pm-2:26 pm

1 stop18h 32m

$131

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/8

8:00 am-3:56 pm

1 stop5h 56m

Lambert-St Louis

Tue 11/11

7:45 pm-9:29 pm

1 stop27h 44m

$150

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/5

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Sat 12/6

7:43 pm-3:06 pm

1 stop21h 23m

$154

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Mon 1/12

5:44 pm-2:33 pm

1 stop22h 49m

$163

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 12/18

6:45 am-10:02 am

1 stop25h 17m

Lambert-St Louis

Mon 1/12

5:44 pm-2:33 pm

1 stop22h 49m

$172

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Mon 1/12

7:43 pm-2:33 pm

2 stops44h 50m

$174

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/8

8:00 am-3:56 pm

1 stop5h 56m

Lambert-St Louis

Tue 11/11

7:45 pm-9:29 pm

1 stop27h 44m

$176

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/5

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Wed 12/10

7:43 pm-11:09 am

1 stop17h 26m

$177

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 12/18

6:45 am-10:02 am

1 stop25h 17m

Lambert-St Louis

Tue 1/13

5:06 pm-2:33 pm

2 stops23h 27m

$241

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 $241.

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 $394. 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 $441. 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 $378 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 $427 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 $351 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 $281 on momondo.

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

As of October 2025, prices for Ontario to St. Louis flights are approximately 0% 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 56m 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 $130Free CancellationRating
5.8
3,122 reviews
Search Frontier flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
8,997 reviews
Search United Airlines flights
American AirlinesPriceFrom $296Free CancellationRating
7.2
11,033 reviews
Search American Airlines flights
DeltaPriceFrom $298Free CancellationRating
7.9
7,996 reviews
Search Delta flights
SouthwestPriceFrom $346Free CancellationRating
8.0
4,236 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
O'Fallon
Wentzville
Collinsville
Fenton
St. Peters
Alton
Farmington
Festus
Glencoe
Edwardsville
Clayton
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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