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Cheap flights from Ontario to St. Louis from $73

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 1/7. Fares may change, and may not be available for all flights or travel dates. Click the price to refresh the search for this deal.
1 adult
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
11:04 am - 9:06 pm
ONT
-
STL
8h 02m1 stop
Frontier Logo
3:46 pm - 11:24 pm
STL
-
ONT
9h 38m1 stop
$141Frontier
Thu, Jan 29 - Sat, Jan 31
Frontier Logo
7:15 am - 2:46 pm
ONT
-
STL
5h 31m1 stop
Frontier Logo
5:44 pm - 9:17 pm
STL
-
ONT
5h 33m1 stop
$148Frontier
Sat, Jan 31 - Mon, Mar 2
Frontier Logo
7:00 am - 10:02 am
ONT
-
STL
25h 02m1 stop
Frontier Logo
7:43 pm - 10:39 pm
STL
-
ONT
28h 56m1 stop
$157Frontier
Tue, Feb 24 - Mon, Mar 2
Frontier Logo
6:00 am - 10:02 am
ONT
-
STL
26h 02m1 stop
Frontier Logo
7:43 pm - 10:39 pm
STL
-
ONT
28h 56m1 stop
$161Frontier
Fri, Feb 20 - Mon, Feb 23
Frontier Logo
10:18 pm - 12:40 pm
ONT
-
STL
12h 22m1 stop
Frontier Logo
7:39 pm - 12:20 am
STL
-
ONT
6h 41m1 stop
$165Frontier
Thu, Jan 15 - Fri, Jan 23
Frontier Logo
11:04 am - 9:06 pm
ONT
-
STL
8h 02m1 stop
Frontier Logo
5:44 pm - 9:17 pm
STL
-
ONT
5h 33m1 stop
$166Frontier
Thu, Feb 5 - Wed, Feb 25
Frontier Logo
10:18 pm - 9:21 pm
ONT
-
STL
21h 03m1 stop
Frontier Logo
9:27 pm - 12:10 pm
STL
-
ONT
16h 43m1 stop
$176Frontier
Thu, Jan 8 - Sun, Jan 25
Frontier Logo
10:18 pm - 2:46 pm
ONT
-
STL
38h 28m2 stops
Frontier Logo
9:27 pm - 2:41 pm
STL
-
ONT
19h 14m1 stop
$177Frontier
Mon, Jan 19 - Sun, Jan 25
Frontier Logo
10:18 pm - 12:12 pm
ONT
-
STL
11h 54m1 stop
Frontier Logo
7:43 pm - 11:56 pm
STL
-
ONT
6h 13m1 stop
$182Frontier
Thu, Jan 8 - Mon, Jan 12
Frontier Logo
1:46 pm - 2:46 pm
ONT
-
STL
23h 00m2 stops
Frontier Logo
9:27 pm - 12:10 pm
STL
-
ONT
16h 43m1 stop
$183Frontier
Fri, Jan 23 - Sun, Jan 25

Alaska Airlines flights from Ontario to St. Louis

Our best Alaska Airlines deals on Ontario to St. Louis flight tickets
Alaska Airlines
Feb 14
ONT6:14 amOntario
30h 09m
1 stop
STL2:23 pmLambert-St Louis
Feb 24
STL7:00 amLambert-St Louis
30h 08m
1 stop
ONT11:08 amOntario
$322
Find similar
Alaska Airlines
Feb 17
ONT6:14 amOntario
29h 37m
1 stop
STL1:51 pmLambert-St Louis
Feb 23
STL2:47 pmLambert-St Louis
22h 21m
1 stop
ONT11:08 amOntario
$354
Find similar

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Jan 29
ONT11:04 amOntario
8h 02m
1 stop
STL9:06 pmLambert-St Louis
Jan 31
STL3:46 pmLambert-St Louis
9h 38m
1 stop
ONT11:24 pmOntario
$141
Find similar
Frontier
Jan 10
ONT3:21 pmOntario
18h 18m
1 stop
STL11:39 amLambert-St Louis
Jan 17
STL3:43 pmLambert-St Louis
9h 16m
1 stop
ONT10:59 pmOntario
$166
Find similar
Frontier
Jan 19
ONT10:18 pmOntario
38h 28m
2 stops
STL2:46 pmLambert-St Louis
Jan 25
STL9:27 pmLambert-St Louis
19h 14m
1 stop
ONT2:41 pmOntario
$177
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 11, 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 1/29

11:04 am-9:06 pm

1 stop8h 02m

Lambert-St Louis

Sat 1/31

3:46 pm-11:24 pm

1 stop9h 38m

$141

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 1/31

7:15 am-2:46 pm

1 stop5h 31m

Lambert-St Louis

Mon 3/2

5:44 pm-9:17 pm

1 stop5h 33m

$148

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/24

7:00 am-10:02 am

1 stop25h 02m

Lambert-St Louis

Mon 3/2

7:43 pm-10:39 pm

1 stop28h 56m

$157

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/20

6:00 am-10:02 am

1 stop26h 02m

Lambert-St Louis

Mon 2/23

7:43 pm-10:39 pm

1 stop28h 56m

$161

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 1/15

10:18 pm-12:40 pm

1 stop12h 22m

Lambert-St Louis

Fri 1/23

7:39 pm-12:20 am

1 stop6h 41m

$165

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/5

11:04 am-9:06 pm

1 stop8h 02m

Lambert-St Louis

Wed 2/25

5:44 pm-9:17 pm

1 stop5h 33m

$166

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 1/8

10:18 pm-9:21 pm

1 stop21h 03m

Lambert-St Louis

Sun 1/25

9:27 pm-12:10 pm

1 stop16h 43m

$176

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 1/19

10:18 pm-2:46 pm

2 stops38h 28m

Lambert-St Louis

Sun 1/25

9:27 pm-2:41 pm

1 stop19h 14m

$177

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 1/8

10:18 pm-12:12 pm

1 stop11h 54m

Lambert-St Louis

Mon 1/12

7:43 pm-11:56 pm

1 stop6h 13m

$182

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 1/23

1:46 pm-2:46 pm

2 stops23h 00m

Lambert-St Louis

Sun 1/25

9:27 pm-12:10 pm

1 stop16h 43m

$183

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, 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 $241. The month of November is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $292.

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 $427. 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 $360 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 $418 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 $358 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 $284 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 35% 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 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 $146Free CancellationRating
5.8
3,084 reviews
Search Frontier flights
DeltaPriceFrom $286Free CancellationRating
7.9
8,008 reviews
Search Delta flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
9,095 reviews
Search United Airlines flights
American AirlinesPriceFrom $292Free CancellationRating
7.2
11,050 reviews
Search American Airlines flights
SouthwestPriceFrom $346Free CancellationRating
7.9
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
St. Peters
Collinsville
Alton
Farmington
Festus
Clayton
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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