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Cheap flights from Ontario to St. Louis from $88

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 5/1. 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
11:44 am - 9:00 pm
ONT
-
STL
7h 16m
1 stop
Frontier Logo
9:55 pm - 8:04 am
STL
-
ONT
12h 09m
1 stop
$190Frontier
Thu, Apr 16 - Sun, Apr 19
Frontier Logo
2:23 pm - 11:19 am
ONT
-
STL
18h 56m
1 stop
Frontier Logo
8:06 pm - 1:28 pm
STL
-
ONT
19h 22m
1 stop
$192Frontier
Tue, Mar 10 - Tue, Mar 17
Frontier Logo
6:20 am - 9:48 am
ONT
-
STL
25h 28m
1 stop
Frontier Logo
8:16 pm - 11:56 pm
STL
-
ONT
5h 40m
1 stop
$197Frontier
Thu, Apr 9 - Mon, Apr 13
Frontier Logo
12:59 am - 7:12 pm
ONT
-
STL
16h 13m
1 stop
Frontier Logo
8:12 pm - 11:55 pm
STL
-
ONT
5h 43m
1 stop
$200Frontier
Thu, Apr 30 - Sat, May 2
Frontier Logo
8:59 pm - 9:00 pm
ONT
-
STL
22h 01m
1 stop
Frontier Logo
8:12 pm - 11:55 pm
STL
-
ONT
5h 43m
1 stop
$201Frontier
Thu, May 7 - Mon, May 11
Frontier Logo
12:59 am - 7:12 pm
ONT
-
STL
16h 13m
1 stop
Frontier Logo
9:55 pm - 8:04 am
STL
-
ONT
12h 09m
1 stop
$207Frontier
Thu, Apr 30 - Sun, May 3
Frontier Logo
11:44 am - 9:00 pm
ONT
-
STL
7h 16m
1 stop
Frontier Logo
3:02 pm - 11:24 pm
STL
-
ONT
10h 22m
1 stop
$211Frontier
Thu, Apr 30 - Mon, May 4
Frontier Logo
11:44 am - 9:00 pm
ONT
-
STL
7h 16m
1 stop
Frontier Logo
8:12 pm - 11:55 pm
STL
-
ONT
5h 43m
1 stop
$212Frontier
Thu, May 7 - Fri, May 8
Frontier Logo
10:50 am - 9:17 pm
ONT
-
STL
8h 27m
1 stop
Frontier Logo
8:16 pm - 11:56 pm
STL
-
ONT
5h 40m
1 stop
$216Frontier
Thu, Apr 2 - Wed, Apr 8
Frontier Logo
5:33 pm - 7:12 pm
ONT
-
STL
23h 39m
1 stop
Frontier Logo
9:55 pm - 8:04 am
STL
-
ONT
12h 09m
1 stop
$219Frontier
Thu, May 14 - Sun, May 17

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Apr 16
ONT11:44 amOntario
7h 16m
1 stop
STL9:00 pmLambert-St Louis
Apr 19
STL9:55 pmLambert-St Louis
12h 09m
1 stop
ONT8:04 amOntario
$190
Frontier
Mar 10
ONT2:23 pmOntario
18h 56m
1 stop
STL11:19 amLambert-St Louis
Mar 17
STL8:06 pmLambert-St Louis
19h 22m
1 stop
ONT1:28 pmOntario
$192
Frontier
Apr 9
ONT6:20 amOntario
25h 28m
1 stop
STL9:48 amLambert-St Louis
Apr 13
STL8:16 pmLambert-St Louis
5h 40m
1 stop
ONT11:56 pmOntario
$197

United Airlines flights from Ontario to St. Louis

Our best United Airlines deals on Ontario to St. Louis flight tickets
United Airlines
Mar 4
ONT6:09 amOntario
8h 49m
2 stops
STL4:58 pmLambert-St Louis
Apr 7
STL8:54 amLambert-St Louis
11h 08m
2 stops
ONT6:02 pmOntario
$447
United Airlines
Mar 3
ONT8:00 amOntario
11h 05m
2 stops
STL9:05 pmLambert-St Louis
Mar 7
STL10:00 amLambert-St Louis
12h 50m
2 stops
ONT8:50 pmOntario
$567
United Airlines
Mar 3
ONT6:10 amOntario
14h 04m
3 stops
STL10:14 pmLambert-St Louis
Mar 7
STL10:00 amLambert-St Louis
12h 50m
2 stops
ONT8:50 pmOntario
$663

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 February 19, 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

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/16

11:44 am-9:00 pm

1 stop7h 16m

Lambert-St Louis

Sun 4/19

9:55 pm-8:04 am

1 stop12h 09m

$190

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 3/10

2:23 pm-11:19 am

1 stop18h 56m

Lambert-St Louis

Tue 3/17

8:06 pm-1:28 pm

1 stop19h 22m

$192

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/9

6:20 am-9:48 am

1 stop25h 28m

Lambert-St Louis

Mon 4/13

8:16 pm-11:56 pm

1 stop5h 40m

$197

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/30

12:59 am-7:12 pm

1 stop16h 13m

Lambert-St Louis

Sat 5/2

8:12 pm-11:55 pm

1 stop5h 43m

$200

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 5/7

8:59 pm-9:00 pm

1 stop22h 01m

Lambert-St Louis

Mon 5/11

8:12 pm-11:55 pm

1 stop5h 43m

$201

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/30

12:59 am-7:12 pm

1 stop16h 13m

Lambert-St Louis

Sun 5/3

9:55 pm-8:04 am

1 stop12h 09m

$207

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/30

11:44 am-9:00 pm

1 stop7h 16m

Lambert-St Louis

Mon 5/4

3:02 pm-11:24 pm

1 stop10h 22m

$211

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 5/7

11:44 am-9:00 pm

1 stop7h 16m

Lambert-St Louis

Fri 5/8

8:12 pm-11:55 pm

1 stop5h 43m

$212

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/2

10:50 am-9:17 pm

1 stop8h 27m

Lambert-St Louis

Wed 4/8

8:16 pm-11:56 pm

1 stop5h 40m

$216

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 5/14

5:33 pm-7:12 pm

1 stop23h 39m

Lambert-St Louis

Sun 5/17

9:55 pm-8:04 am

1 stop12h 09m

$219

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 Wednesday when prices can be found for as low as $386. 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 Sunday because tickets tend to average around $428. 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 $351 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 $425 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 $259 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 12m

Direct flights

None
The fastest flight from Ontario to St. Louis takes 5h 12m
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 12m 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
8,212 reviews
Search Delta flights
FrontierPriceFrom $146Free CancellationRating
5.7
3,048 reviews
Search Frontier flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
9,321 reviews
Search United Airlines flights
American AirlinesPriceFrom $292Free CancellationRating
7.2
11,313 reviews
Search American Airlines flights
SouthwestPriceFrom $340Free CancellationRating
8.0
4,295 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
Collinsville
St. Peters
Fenton
Wentzville
Alton
Farmington
Clayton
Edwardsville
Eureka
Festus
Litchfield
Glencoe
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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