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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 1/25. 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
6:15 am - 12:12 pmONT-STL
27h 57m1 stop
Frontier Logo
1:16 pm - 9:17 pmSTL-ONT
10h 01m1 stop
$130Frontier
Find Deal
Sat, Dec 13 - Mon, Dec 15
Frontier Logo
6:15 am - 9:48 pmONT-STL
13h 33m1 stop
Frontier Logo
1:16 pm - 9:17 pmSTL-ONT
10h 01m1 stop
$134Frontier
Find Deal
Fri, Dec 12 - Mon, Dec 15
Frontier Logo
6:15 am - 12:12 pmONT-STL
27h 57m1 stop
Frontier Logo
7:43 pm - 3:06 pmSTL-ONT
21h 23m1 stop
$138Frontier
Find Deal
Sat, Dec 6 - Sat, Dec 13
Frontier Logo
12:58 am - 6:58 pmONT-STL
16h 00m1 stop
Frontier Logo
9:54 pm - 9:06 pmSTL-ONT
25h 12m1 stop
$144Frontier
Find Deal
Wed, Nov 26 - Sun, Nov 30
Frontier Logo
6:30 am - 9:09 pmONT-STL
12h 39m1 stop
Frontier Logo
7:43 pm - 11:09 amSTL-ONT
17h 26m1 stop
$145Frontier
Find Deal
Wed, Nov 26 - Wed, Dec 3
Frontier Logo
7:08 pm - 6:58 pmONT-STL
21h 50m1 stop
Frontier Logo
9:54 pm - 9:06 pmSTL-ONT
25h 12m1 stop
$146Frontier
Find Deal
Sat, Nov 22 - Sun, Nov 23
Delta Logo
5:49 pm - 9:10 amONT-STL
13h 21m2 stops
Delta Logo
6:00 am - 5:07 pmSTL-ONT
13h 07m2 stops
$276Delta
Find Deal
Sat, Dec 6 - Sat, Dec 13
Multiple Airlines Logo
7:10 am - 10:47 pmONT-STL
13h 37m2 stops
Multiple Airlines Logo
1:16 pm - 9:17 pmSTL-ONT
10h 01m1 stop
$306Multiple Airlines
Find Deal
Sat, Dec 13 - Mon, Dec 15
Delta Logo
6:40 am - 7:10 pmONT-STL
10h 30m2 stops
Delta Logo
2:20 pm - 10:47 pmSTL-ONT
10h 27m2 stops
$317Delta
Find Deal
Fri, Dec 12 - Mon, Dec 15
American Airlines Logo
4:47 pm - 11:56 pmONT-STL
5h 09m1 stop
American Airlines Logo
9:30 am - 1:55 pmSTL-ONT
6h 25m1 stop
$328American Airlines
Find Deal
Thu, Dec 11 - Wed, Dec 17

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Dec 13
ONT6:15 amOntario
27h 57m
1 stop
STL12:12 pmLambert-St Louis
Dec 15
STL1:16 pmLambert-St Louis
10h 01m
1 stop
ONT9:17 pmOntario
$130
Find similar
Frontier
Dec 12
ONT6:15 amOntario
13h 33m
1 stop
STL9:48 pmLambert-St Louis
Dec 15
STL1:16 pmLambert-St Louis
10h 01m
1 stop
ONT9:17 pmOntario
$134
Find similar
Frontier
Dec 6
ONT6:15 amOntario
27h 57m
1 stop
STL12:12 pmLambert-St Louis
Dec 13
STL7:43 pmLambert-St Louis
21h 23m
1 stop
ONT3:06 pmOntario
$138
Find similar

Delta flights from Ontario to St. Louis

Our best Delta deals on Ontario to St. Louis flight tickets
Delta
Dec 6
ONT5:49 pmOntario
13h 21m
2 stops
STL9:10 amLambert-St Louis
Dec 13
STL6:00 amLambert-St Louis
13h 07m
2 stops
ONT5:07 pmOntario
$276
Find similar
Delta
Dec 12
ONT6:40 amOntario
10h 30m
2 stops
STL7:10 pmLambert-St Louis
Dec 15
STL2:20 pmLambert-St Louis
10h 27m
2 stops
ONT10:47 pmOntario
$317
Find similar
Delta
Dec 18
ONT5:49 pmOntario
13h 21m
2 stops
STL9:10 amLambert-St Louis
Jan 1
STL7:20 amLambert-St Louis
7h 09m
1 stop
ONT12:29 pmOntario
$322
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 November 10, 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

Sat 12/13

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Mon 12/15

1:16 pm-9:17 pm

1 stop10h 01m

$130

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

6:15 am-9:48 pm

1 stop13h 33m

Lambert-St Louis

Mon 12/15

1:16 pm-9:17 pm

1 stop10h 01m

$134

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/6

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Sat 12/13

7:43 pm-3:06 pm

1 stop21h 23m

$138

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 11/26

12:58 am-6:58 pm

1 stop16h 00m

Lambert-St Louis

Sun 11/30

9:54 pm-9:06 pm

1 stop25h 12m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 11/26

6:30 am-9:09 pm

1 stop12h 39m

Lambert-St Louis

Wed 12/3

7:43 pm-11:09 am

1 stop17h 26m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 11/22

7:08 pm-6:58 pm

1 stop21h 50m

Lambert-St Louis

Sun 11/23

9:54 pm-9:06 pm

1 stop25h 12m

$146

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/6

5:49 pm-9:10 am

2 stops13h 21m

Lambert-St Louis

Sat 12/13

6:00 am-5:07 pm

2 stops13h 07m

$276

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/13

7:10 am-10:47 pm

2 stops13h 37m

Lambert-St Louis

Mon 12/15

1:16 pm-9:17 pm

1 stop10h 01m

$306

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

6:40 am-7:10 pm

2 stops10h 30m

Lambert-St Louis

Mon 12/15

2:20 pm-10:47 pm

2 stops10h 27m

$317

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 12/11

4:47 pm-11:56 pm

1 stop5h 09m

Lambert-St Louis

Wed 12/17

9:30 am-1:55 pm

1 stop6h 25m

$328

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

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 $391. 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 Monday because tickets tend to average around $431. 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 $375 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 $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 $296 on momondo.

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

As of November 2025, prices for Ontario to St. Louis flights are approximately 88% 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 09m 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
3,113 reviews
Search Frontier flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
9,012 reviews
Search United Airlines flights
American AirlinesPriceFrom $296Free CancellationRating
7.2
11,045 reviews
Search American Airlines flights
DeltaPriceFrom $298Free CancellationRating
7.9
8,007 reviews
Search Delta flights
SouthwestPriceFrom $340Free CancellationRating
8.0
4,235 reviews
Search Southwest flights

  • Southwest Flights From Ontario to St. Louis

    Southwest operates around 1 flight 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 $340 round-trip. Southwest has been scored 8.0/10 in 4,235 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
Wentzville
Fenton
Collinsville
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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