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Cheap flights from Ontario to St. Louis from $67

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 12/10. 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 - 10:02 am
ONT
-
STL
26h 02m1 stop
Frontier Logo
7:43 pm - 10:59 pm
STL
-
ONT
29h 16m1 stop
$134Frontier
Fri, Jan 9 - Mon, Jan 12
Frontier Logo
7:15 am - 2:46 pm
ONT
-
STL
5h 31m1 stop
Frontier Logo
3:46 pm - 11:24 pm
STL
-
ONT
9h 38m1 stop
$148Frontier
Wed, Jan 21 - Sat, Jan 24
Frontier Logo
6:20 am - 6:44 pm
ONT
-
STL
10h 24m1 stop
Frontier Logo
9:45 pm - 12:42 pm
STL
-
ONT
16h 57m1 stop
$149Frontier
Fri, Feb 6 - Mon, Feb 9
Frontier Logo
6:00 am - 10:02 am
ONT
-
STL
26h 02m1 stop
Frontier Logo
5:11 pm - 5:54 pm
STL
-
ONT
26h 43m2 stops
$153Frontier
Fri, Jan 9 - Mon, Jan 12
Frontier Logo
3:07 pm - 9:06 pm
ONT
-
STL
27h 59m1 stop
Frontier Logo
9:32 pm - 12:10 pm
STL
-
ONT
16h 38m1 stop
$157Frontier
Wed, Jan 28 - Sun, Feb 1
Frontier Logo
2:34 pm - 6:51 am
ONT
-
STL
38h 17m2 stops
Frontier Logo
3:43 pm - 10:59 pm
STL
-
ONT
9h 16m1 stop
$163Frontier
Mon, Jan 12 - Wed, Jan 14
Frontier Logo
8:30 am - 4:49 pm
ONT
-
STL
6h 19m1 stop
Frontier Logo
7:43 pm - 11:59 pm
STL
-
ONT
6h 16m1 stop
$165Frontier
Wed, Mar 4 - Mon, Mar 9
Frontier Logo
10:45 am - 12:12 pm
ONT
-
STL
23h 27m1 stop
Frontier Logo
7:43 pm - 10:59 pm
STL
-
ONT
29h 16m1 stop
$167Frontier
Wed, Jan 7 - Mon, Jan 12
Frontier Logo
10:45 am - 12:12 pm
ONT
-
STL
23h 27m1 stop
Frontier Logo
7:43 pm - 10:59 pm
STL
-
ONT
29h 16m1 stop
$169Frontier
Wed, Jan 7 - Mon, Jan 12
Frontier Logo
6:00 am - 10:02 am
ONT
-
STL
26h 02m1 stop
Frontier Logo
5:11 pm - 5:54 pm
STL
-
ONT
26h 43m2 stops
$172Frontier
Fri, Jan 9 - Tue, Jan 13

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Jan 9
ONT6:00 amOntario
26h 02m
1 stop
STL10:02 amLambert-St Louis
Jan 12
STL7:43 pmLambert-St Louis
29h 16m
1 stop
ONT10:59 pmOntario
$134
Find similar
Frontier
Jan 21
ONT7:15 amOntario
5h 31m
1 stop
STL2:46 pmLambert-St Louis
Jan 24
STL3:46 pmLambert-St Louis
9h 38m
1 stop
ONT11:24 pmOntario
$148
Find similar
Frontier
Feb 6
ONT6:20 amOntario
10h 24m
1 stop
STL6:44 pmLambert-St Louis
Feb 9
STL9:45 pmLambert-St Louis
16h 57m
1 stop
ONT12:42 pmOntario
$149
Find similar

Southwest flights from Ontario to St. Louis

Our best Southwest deals on Ontario to St. Louis flight tickets
Southwest
Jan 7
ONT5:55 amOntario
9h 15m
2 stops
STL5:10 pmLambert-St Louis
Jan 12
STL6:05 amLambert-St Louis
12h 00m
2 stops
ONT4:05 pmOntario
$254
Find similar
Southwest
Dec 18
ONT8:25 amOntario
8h 50m
2 stops
STL7:15 pmLambert-St Louis
Dec 22
STL3:45 pmLambert-St Louis
8h 15m
2 stops
ONT10:00 pmOntario
$567
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 December 4, 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

Fri 1/9

6:00 am-10:02 am

1 stop26h 02m

Lambert-St Louis

Mon 1/12

7:43 pm-10:59 pm

1 stop29h 16m

$134

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/21

7:15 am-2:46 pm

1 stop5h 31m

Lambert-St Louis

Sat 1/24

3:46 pm-11:24 pm

1 stop9h 38m

$148

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/6

6:20 am-6:44 pm

1 stop10h 24m

Lambert-St Louis

Mon 2/9

9:45 pm-12:42 pm

1 stop16h 57m

$149

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 1/9

6:00 am-10:02 am

1 stop26h 02m

Lambert-St Louis

Mon 1/12

5:11 pm-5:54 pm

2 stops26h 43m

$153

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/28

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sun 2/1

9:32 pm-12:10 pm

1 stop16h 38m

$157

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 1/12

2:34 pm-6:51 am

2 stops38h 17m

Lambert-St Louis

Wed 1/14

3:43 pm-10:59 pm

1 stop9h 16m

$163

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 3/4

8:30 am-4:49 pm

1 stop6h 19m

Lambert-St Louis

Mon 3/9

7:43 pm-11:59 pm

1 stop6h 16m

$165

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/7

10:45 am-12:12 pm

1 stop23h 27m

Lambert-St Louis

Mon 1/12

7:43 pm-10:59 pm

1 stop29h 16m

$167

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/7

10:45 am-12:12 pm

1 stop23h 27m

Lambert-St Louis

Mon 1/12

7:43 pm-10:59 pm

1 stop29h 16m

$169

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 1/9

6:00 am-10:02 am

1 stop26h 02m

Lambert-St Louis

Tue 1/13

5:11 pm-5:54 pm

2 stops26h 43m

$172

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 $388. 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 $361 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 $421 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 $348 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 December 2025, prices for Ontario to St. Louis flights are approximately 36% 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

Fastest flight time

5h 09m

Direct flights

None
The fastest flight from Ontario to St. Louis takes 5h 09m
There are no direct flights from Ontario to St. Louis. There are no popular flight routes from Ontario to St. Louis.
Search flight deals

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

    There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 14m 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 $146Free CancellationRating
5.8
3,092 reviews
Search Frontier flights
DeltaPriceFrom $286Free CancellationRating
7.9
8,010 reviews
Search Delta flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
9,062 reviews
Search United Airlines flights
American AirlinesPriceFrom $292Free CancellationRating
7.2
11,045 reviews
Search American Airlines flights
SouthwestPriceFrom $346Free CancellationRating
8.0
4,253 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
O'Fallon
Florissant
Fenton
Wentzville
Collinsville
St. Peters
Alton
Farmington
Clayton
Festus
Glencoe
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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