What is the cheapest airline that flies from Ontario to Lambert-St Louis?

Frontier is the most popular carrier operating from Ontario to Lambert-St Louis

Which layover airport has the shortest travel time from Ontario to St. Louis?

Flights connecting via Phoenix (PHX) have the shortest average one-way travel time: 5h 07m.

Which layover airport offers the lowest fares from Ontario to St. Louis?

Flights via Denver (DEN) offer the lowest average round-trip price of $267.

Which airport is the most popular layover for flights between Ontario and St. Louis?

Denver (DEN) was the most common stop: 78% of momondo users choosing 1-stop flights on this route connected there.

Which layover airport has the shortest connection time from Ontario to St. Louis?

Phoenix (PHX) has the shortest average layover time for this route: 0h 56m.

What airlines fly to St. Louis?

Southwest, American Airlines and Frontier are the top three most popular airlines that fly to St. Louis from Ontario according to our data. Southwest is the first choice among our users, with 50% of people opting to fly with this airline when traveling to St. Louis. Keep in mind that there are 6 different airlines that fly to St. Louis on a routine basis, so you have a few additional options to choose from.

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?

There are 5 operators available for flights from Ontario Airport to Lambert-St Louis Airport as of January 2026.

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.

$74 Cheap Flights from Ontario to St. Louis in 2026

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Find the cheapest flights from Ontario to St. Louis

Round-trip

One-way

Last minute

Cheap round-trip flights

Enter your travel dates to find the best prices.

7:22 pm - 9:26 pm

ONT

STL

24h 04m

1 stop

2:51 pm - 7:59 am

STL

ONT

19h 08m

1 stop

$141Frontier

Thu, Feb 19 - Sat, Feb 21

7:17 pm - 9:26 pm

ONT

STL

24h 09m

1 stop

2:51 pm - 7:59 am

STL

ONT

19h 08m

1 stop

$149Frontier

Wed, Feb 18 - Sat, Feb 21

8:36 am - 1:58 pm

ONT

STL

27h 22m

1 stop

4:51 pm - 9:34 am

STL

ONT

18h 43m

1 stop

$162Frontier

Tue, Feb 10 - Wed, Feb 18

8:40 am - 3:53 pm

ONT

STL

5h 13m

1 stop

2:51 pm - 11:59 pm

STL

ONT

11h 08m

1 stop

$164Frontier

Wed, Feb 25 - Sat, Feb 28

8:36 am - 1:58 pm

ONT

STL

27h 22m

1 stop

4:51 pm - 9:34 am

STL

ONT

18h 43m

1 stop

$173Frontier

Tue, Feb 10 - Wed, Feb 18

1:05 pm - 8:50 pm

ONT

STL

5h 45m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$180Frontier

Mon, Feb 2 - Sat, Feb 7

7:22 pm - 9:26 pm

ONT

STL

24h 04m

1 stop

10:11 pm - 1:52 pm

STL

ONT

17h 41m

1 stop

$181Frontier

Thu, Feb 19 - Mon, Feb 23

3:22 pm - 1:58 pm

ONT

STL

20h 36m

2 stops

4:51 pm - 9:34 am

STL

ONT

18h 43m

1 stop

$190Frontier

Tue, Feb 10 - Wed, Feb 18

6:00 am - 1:56 pm

ONT

STL

5h 56m

1 stop

2:51 pm - 7:59 am

STL

ONT

19h 08m

1 stop

$196Frontier

Sat, Feb 14 - Sat, Feb 21

7:15 am - 2:46 pm

ONT

STL

5h 31m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$201Frontier

Wed, Feb 4 - Sat, Feb 7

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets

Frontier

Feb 19

ONT7:22 pmOntario

24h 04m

1 stop

STL9:26 pmLambert-St Louis

Feb 21

STL2:51 pmLambert-St Louis

19h 08m

1 stop

ONT7:59 amOntario

$141

Frontier

Feb 18

ONT7:17 pmOntario

24h 09m

1 stop

STL9:26 pmLambert-St Louis

Feb 21

STL2:51 pmLambert-St Louis

19h 08m

1 stop

ONT7:59 amOntario

$149

Frontier

Feb 10

ONT8:36 amOntario

27h 22m

1 stop

STL1:58 pmLambert-St Louis

Feb 18

STL4:51 pmLambert-St Louis

18h 43m

1 stop

ONT9:34 amOntario

$162

United Airlines flights from Ontario to St. Louis

Our best United Airlines deals on Ontario to St. Louis flight tickets

United Airlines

Feb 10

ONT1:24 pmOntario

5h 34m

1 stop

STL8:58 pmLambert-St Louis

Feb 24

STL4:28 pmLambert-St Louis

7h 32m

1 stop

ONT10:00 pmOntario

$257

United Airlines

Apr 15

ONT1:34 pmOntario

5h 20m

1 stop

STL8:54 pmLambert-St Louis

Apr 21

STL8:54 amLambert-St Louis

11h 08m

2 stops

ONT6:02 pmOntario

$262

United Airlines

Apr 15

ONT11:05 amOntario

9h 51m

2 stops

STL10:56 pmLambert-St Louis

Apr 21

STL11:15 amLambert-St Louis

11h 21m

2 stops

ONT8:36 pmOntario

$268

Fly from

Fly to

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/19

7:22 pm-9:26 pm

1 stop24h 04m

Lambert-St Louis

Sat 2/21

2:51 pm-7:59 am

1 stop19h 08m

$141

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/18

7:17 pm-9:26 pm

1 stop24h 09m

Lambert-St Louis

Sat 2/21

2:51 pm-7:59 am

1 stop19h 08m

$149

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/10

8:36 am-1:58 pm

1 stop27h 22m

Lambert-St Louis

Wed 2/18

4:51 pm-9:34 am

1 stop18h 43m

$162

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/25

8:40 am-3:53 pm

1 stop5h 13m

Lambert-St Louis

Sat 2/28

2:51 pm-11:59 pm

1 stop11h 08m

$164

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/10

8:36 am-1:58 pm

1 stop27h 22m

Lambert-St Louis

Wed 2/18

4:51 pm-9:34 am

1 stop18h 43m

$173

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 2/2

1:05 pm-8:50 pm

1 stop5h 45m

Lambert-St Louis

Sat 2/7

3:46 pm-11:24 pm

1 stop9h 38m

$180

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/19

7:22 pm-9:26 pm

1 stop24h 04m

Lambert-St Louis

Mon 2/23

10:11 pm-1:52 pm

1 stop17h 41m

$181

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 2/10

3:22 pm-1:58 pm

2 stops20h 36m

Lambert-St Louis

Wed 2/18

4:51 pm-9:34 am

1 stop18h 43m

$190

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 2/14

6:00 am-1:56 pm

1 stop5h 56m

Lambert-St Louis

Sat 2/21

2:51 pm-7:59 am

1 stop19h 08m

$196

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

7:15 am-2:46 pm

1 stop5h 31m

Lambert-St Louis

Sat 2/7

3:46 pm-11:24 pm

1 stop9h 38m

$201

Flights are sorted by cheapest round-trip flights first.

Showing 1-10 of 20 resultsSorted by cheapest first

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

Prices

Airlines

Layovers

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 Friday 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 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 $408 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 $280 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?
There are 5 operators available for flights from Ontario Airport to Lambert-St Louis Airport as of January 2026.
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?
momondo data reveals that the most frequently booked airline on the route from Ontario to St. Louis is Frontier, representing 47% of all bookings. The subsequent popular airlines are Southwest at 22%, American Airlines at 18%, and Delta at 7%.

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
Frontier	PriceFrom $131	Free Cancellation	Rating 5.7 3,058 reviews	Search Frontier flights
Delta	PriceFrom $139	Free Cancellation	Rating 7.9 8,075 reviews	Search Delta flights
United Airlines	PriceFrom $292	Free Cancellation	Rating 7.4 9,176 reviews	Search United Airlines flights
American Airlines	PriceFrom $292	Free Cancellation	Rating 7.2 11,160 reviews	Search American Airlines flights
Southwest	PriceFrom $346	Free Cancellation	Rating 8.0 4,262 reviews	Search Southwest flights

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Chesterfield

Hermann

Fairview Heights

Maryland Heights

Florissant

O'Fallon

Fenton

Collinsville

St. Peters

Wentzville

Alton

Farmington

Clayton

Eureka

Edwardsville

Festus

Glencoe

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.