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Cheap flights from Ontario to St. Louis from $132

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 9/1. 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
6:00 am - 7:23 pm
ONT
-
STL
11h 23m
1 stop
Frontier Logo
8:08 pm - 11:50 pm
STL
-
ONT
5h 42m
1 stop
$230Frontier
Wed, Aug 12 - Sat, Aug 15
Frontier Logo
10:49 am - 7:23 pm
ONT
-
STL
6h 34m
1 stop
Frontier Logo
7:03 pm - 7:53 pm
STL
-
ONT
26h 50m
1 stop
$241Frontier
Tue, Aug 4 - Tue, Aug 11
Frontier Logo
10:49 am - 7:23 pm
ONT
-
STL
6h 34m
1 stop
Frontier Logo
3:34 pm - 10:03 am
STL
-
ONT
20h 29m
2 stops
$255Frontier
Tue, Aug 4 - Tue, Aug 11
Frontier Logo
6:00 am - 7:23 pm
ONT
-
STL
11h 23m
1 stop
Frontier Logo
4:57 pm - 10:04 am
STL
-
ONT
43h 07m
2 stops
$261Frontier
Tue, Jul 7 - Mon, Jul 20
Frontier Logo
3:34 pm - 7:36 pm
ONT
-
STL
26h 02m
1 stop
Frontier Logo
8:08 pm - 10:05 am
STL
-
ONT
15h 57m
1 stop
$262Frontier
Thu, Aug 27 - Tue, Sep 1
Frontier Logo
9:49 pm - 7:15 pm
ONT
-
STL
19h 26m
2 stops
Frontier Logo
8:10 pm - 10:43 am
STL
-
ONT
16h 33m
1 stop
$264Frontier
Wed, Oct 7 - Tue, Oct 13
Frontier Logo
6:00 am - 7:23 pm
ONT
-
STL
11h 23m
1 stop
Frontier Logo
8:08 pm - 7:51 pm
STL
-
ONT
25h 43m
2 stops
$268Frontier
Wed, Jun 24 - Tue, Jun 30
Frontier Logo
6:00 am - 7:23 pm
ONT
-
STL
11h 23m
1 stop
Frontier Logo
8:08 pm - 10:03 am
STL
-
ONT
15h 55m
1 stop
$269Frontier
Wed, Aug 12 - Sun, Aug 16
Frontier Logo
1:28 pm - 6:05 pm
ONT
-
STL
26h 37m
1 stop
Frontier Logo
8:08 pm - 10:03 am
STL
-
ONT
15h 55m
1 stop
$270Frontier
Tue, Jul 7 - Tue, Jul 14
Frontier Logo
3:34 pm - 7:23 pm
ONT
-
STL
25h 49m
2 stops
Frontier Logo
8:08 pm - 10:05 am
STL
-
ONT
15h 57m
1 stop
$272Frontier
Tue, Jun 16 - Tue, Jun 23

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Aug 12
ONT6:00 amOntario
11h 23m
1 stop
STL7:23 pmLambert-St Louis
Aug 15
STL8:08 pmLambert-St Louis
5h 42m
1 stop
ONT11:50 pmOntario
$230
Frontier
Aug 4
ONT10:49 amOntario
6h 34m
1 stop
STL7:23 pmLambert-St Louis
Aug 11
STL7:03 pmLambert-St Louis
26h 50m
1 stop
ONT7:53 pmOntario
$241
Frontier
Aug 4
ONT10:49 amOntario
6h 34m
1 stop
STL7:23 pmLambert-St Louis
Aug 11
STL3:34 pmLambert-St Louis
20h 29m
2 stops
ONT10:03 amOntario
$255

Delta flights from Ontario to St. Louis

Our best Delta deals on Ontario to St. Louis flight tickets
Delta
Jun 4
ONT4:57 pmOntario
5h 33m
1 stop
STL12:30 amLambert-St Louis
Jun 10
STL7:55 pmLambert-St Louis
5h 54m
1 stop
ONT11:49 pmOntario
$524
Delta
May 28
ONT6:00 amOntario
5h 32m
1 stop
STL1:32 pmLambert-St Louis
Jun 6
STL7:00 amLambert-St Louis
7h 19m
1 stop
ONT12:19 pmOntario
$534

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 May 22, 2026.
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

Cheapest round-trip
Quickest round-trip

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 8/12

6:00 am-7:23 pm

1 stop11h 23m

Lambert-St Louis

Sat 8/15

8:08 pm-11:50 pm

1 stop5h 42m

$230

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/4

10:49 am-7:23 pm

1 stop6h 34m

Lambert-St Louis

Tue 8/11

7:03 pm-7:53 pm

1 stop26h 50m

$241

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/4

10:49 am-7:23 pm

1 stop6h 34m

Lambert-St Louis

Tue 8/11

3:34 pm-10:03 am

2 stops20h 29m

$255

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 7/7

6:00 am-7:23 pm

1 stop11h 23m

Lambert-St Louis

Mon 7/20

4:57 pm-10:04 am

2 stops43h 07m

$261

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 8/27

3:34 pm-7:36 pm

1 stop26h 02m

Lambert-St Louis

Tue 9/1

8:08 pm-10:05 am

1 stop15h 57m

$262

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 10/7

9:49 pm-7:15 pm

2 stops19h 26m

Lambert-St Louis

Tue 10/13

8:10 pm-10:43 am

1 stop16h 33m

$264

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 6/24

6:00 am-7:23 pm

1 stop11h 23m

Lambert-St Louis

Tue 6/30

8:08 pm-7:51 pm

2 stops25h 43m

$268

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 8/12

6:00 am-7:23 pm

1 stop11h 23m

Lambert-St Louis

Sun 8/16

8:08 pm-10:03 am

1 stop15h 55m

$269

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 7/7

1:28 pm-6:05 pm

1 stop26h 37m

Lambert-St Louis

Tue 7/14

8:08 pm-10:03 am

1 stop15h 55m

$270

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 6/16

3:34 pm-7:23 pm

2 stops25h 49m

Lambert-St Louis

Tue 6/23

8:08 pm-10:05 am

1 stop15h 57m

$272

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, September 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 $247. The month of April is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $250.

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 Wednesday when prices can be found for as low as $399. 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 $528. 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 $331 when looking at flights departing in the evening. At noon is when there is more demand to fly to St. Louis, so prices are often more expensive at around $501 per ticket.

How far in advance should I book a flight from Ontario 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 $324 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 $240 on momondo.

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

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

Fastest flight time

5h 32m

Direct flights

None
The fastest flight from Ontario to St. Louis takes 5h 32m
There are no direct flights from Ontario to St. Louis. There are no popular flight routes from Ontario to St. Louis.
Search flight deals

Frequently asked questions about flying from Ontario to St. Louis

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

    There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 32m 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
DeltaPriceFrom $139Free CancellationRating
7.9
8,449 reviews
Search Delta flights
FrontierPriceFrom $160Free CancellationRating
5.6
2,944 reviews
Search Frontier flights
United AirlinesPriceFrom $249Free CancellationRating
7.4
9,751 reviews
Search United Airlines flights
American AirlinesPriceFrom $292Free CancellationRating
7.1
11,644 reviews
Search American Airlines flights
SouthwestPriceFrom $316Free CancellationRating
7.9
4,277 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
St. Peters
Collinsville
Alton
Wentzville
Fenton
Farmington
Festus
Eureka
Clayton
Litchfield
Edwardsville
Shrewsbury
Grafton

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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