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

Frontier, Hawaiian Airlines, and Alaska Airlines are the most popular carriers operating from Ontario to Lambert-St Louis

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

Flights connecting via Atlanta (ATL) have the shortest average one-way travel time: 6h 29m.

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

Denver (DEN) was the most common stop: 89% of momondo users choosing 1-stop flights on this route connected there.

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

Flights via Denver (DEN) offer the lowest average round-trip price of $279.

How many flights depart from Ontario to St. Louis on average per week?

As of August 2025, 3 flights take off from Ontario and land in St. Louis each week. The most common flight departure day for this route is Mon, with 33% of weekly flights taking off on this day.

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

Atlanta (ATL) has the shortest average layover time for this route: 1h 05m.

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 44% 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 August 2025.

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.

$71 Cheap Flights from Ontario to St. Louis (ONT-STL) in 2025

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Find the cheapest flights from Ontario to St. Louis (ONT-STL)

Round-trip

One-way

Last minute

Cheap round-trip flights

6:00 am - 1:57 pmONT-STL

5h 57m1 stop

7:45 pm - 11:50 pmSTL-ONT

6h 05m1 stop

$142Frontier

Find Deal

Thu, Oct 30 - Mon, Nov 3

8:59 pm - 9:06 amONT-STL

10h 07m1 stop

7:55 pm - 7:23 amSTL-ONT

13h 28m1 stop

$143Frontier

Find Deal

Wed, Sep 10 - Thu, Sep 11

8:59 pm - 9:06 amONT-STL

10h 07m1 stop

2:38 pm - 8:56 pmSTL-ONT

8h 18m1 stop

$144Frontier

Find Deal

Fri, Sep 12 - Mon, Sep 15

9:16 am - 1:53 pmONT-STL

26h 37m1 stop

9:59 pm - 8:42 pmSTL-ONT

24h 43m1 stop

$145Frontier

Find Deal

Thu, Oct 2 - Mon, Oct 13

6:53 am - 9:07 amONT-STL

24h 14m1 stop

6:33 am - 12:37 pmSTL-ONT

8h 04m1 stop

$237

Find Deal

Wed, Oct 22 - Sat, Oct 25

1:10 pm - 10:50 pmONT-STL

7h 40m2 stops

5:18 am - 10:05 amSTL-ONT

6h 47m1 stop

$298American Airlines

Find Deal

Tue, Sep 16 - Thu, Sep 18

6:10 am - 6:22 pmONT-STL

10h 12m2 stops

5:18 am - 11:56 amSTL-ONT

8h 38m2 stops

$303American Airlines

Find Deal

Tue, Sep 23 - Tue, Sep 30

8:30 am - 5:15 pmONT-STL

6h 45m2 stops

10:25 am - 3:20 pmSTL-ONT

6h 55m2 stops

$327Southwest

Find Deal

Tue, Nov 4 - Wed, Nov 5

5:50 pm - 8:51 amONT-STL

13h 01m2 stops

6:50 am - 5:09 pmSTL-ONT

12h 19m2 stops

$350Delta

Find Deal

Fri, Nov 7 - Tue, Nov 11

4:49 pm - 12:46 amONT-STL

5h 57m1 stop

4:50 pm - 10:41 pmSTL-ONT

7h 51m1 stop

$358Delta

Find Deal

Mon, Nov 24 - Tue, Dec 2

Frontier flights from Ontario to St. Louis

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

Frontier

Oct 30

ONT6:00 amOntario

5h 57m

1 stop

STL1:57 pmLambert-St Louis

Nov 3

STL7:45 pmLambert-St Louis

6h 05m

1 stop

ONT11:50 pmOntario

$142

Find similar

Frontier

Sep 10

ONT8:59 pmOntario

10h 07m

1 stop

STL9:06 amLambert-St Louis

Sep 11

STL7:55 pmLambert-St Louis

13h 28m

1 stop

ONT7:23 amOntario

$143

Find similar

Frontier

Sep 12

ONT8:59 pmOntario

10h 07m

1 stop

STL9:06 amLambert-St Louis

Sep 15

STL2:38 pmLambert-St Louis

8h 18m

1 stop

ONT8:56 pmOntario

$144

Find similar

Alaska Airlines flights from Ontario to St. Louis

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

Alaska Airlines

Oct 21

ONT1:31 pmOntario

8h 32m

1 stop

STL12:03 amLambert-St Louis

Oct 24

STL3:57 pmLambert-St Louis

10h 06m

1 stop

ONT12:03 amOntario

$336

Find similar

Alaska Airlines

Sep 3

ONT6:00 amOntario

9h 34m

1 stop

STL5:34 pmLambert-St Louis

Sep 15

STL6:30 pmLambert-St Louis

18h 14m

1 stop

ONT10:44 amOntario

$440

Find similar

Fly from

Fly to

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/30

6:00 am-1:57 pm

1 stop5h 57m

Lambert-St Louis

Mon 11/3

7:45 pm-11:50 pm

1 stop6h 05m

$142

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 9/10

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Thu 9/11

7:55 pm-7:23 am

1 stop13h 28m

$143

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 9/12

8:59 pm-9:06 am

1 stop10h 07m

Lambert-St Louis

Mon 9/15

2:38 pm-8:56 pm

1 stop8h 18m

$144

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 10/2

9:16 am-1:53 pm

1 stop26h 37m

Lambert-St Louis

Mon 10/13

9:59 pm-8:42 pm

1 stop24h 43m

$145

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 10/22

6:53 am-9:07 am

1 stop24h 14m

Lambert-St Louis

Sat 10/25

6:33 am-12:37 pm

1 stop8h 04m

$237

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 9/16

1:10 pm-10:50 pm

2 stops7h 40m

Lambert-St Louis

Thu 9/18

5:18 am-10:05 am

1 stop6h 47m

$298

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 9/23

6:10 am-6:22 pm

2 stops10h 12m

Lambert-St Louis

Tue 9/30

5:18 am-11:56 am

2 stops8h 38m

$303

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 11/4

8:30 am-5:15 pm

2 stops6h 45m

Lambert-St Louis

Wed 11/5

10:25 am-3:20 pm

2 stops6h 55m

$327

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 11/7

5:50 pm-8:51 am

2 stops13h 01m

Lambert-St Louis

Tue 11/11

6:50 am-5:09 pm

2 stops12h 19m

$350

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 11/24

4:49 pm-12:46 am

1 stop5h 57m

Lambert-St Louis

Tue 12/2

4:50 pm-10:41 pm

1 stop7h 51m

$358

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

Other information

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 $298. The month of October is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $298.

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 Tuesday when prices can be found for as low as $391. 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 Saturday because tickets tend to average around $458. 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 $396 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 $427 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 $356 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 $281 on momondo.

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

As of August 2025, prices for Ontario to St. Louis flights are approximately 7% 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

Direct flights	None

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 04m 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 August 2025.
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 8%.

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 5.8 3,200 reviews	Search Frontier flights
Delta	PriceFrom $298	Free Cancellation	Rating 7.9 7,979 reviews	Search Delta flights
American Airlines	PriceFrom $306	Free Cancellation	Rating 7.2 10,000 reviews	Search American Airlines flights
Southwest	PriceFrom $340	Free Cancellation	Rating 8.0 4,242 reviews	Search Southwest flights
United Airlines	PriceFrom $346	Free Cancellation	Rating 7.4 8,943 reviews	Search United Airlines flights

Southwest Flights From Ontario to St. Louis
Southwest operates around 3 flights from Ontario to St. Louis every week. The average price of these flights found in the last 72 hours has been $417, but momondo users have found Southwest deals from Ontario to St. Louis from as low as $340 round-trip. Southwest has been scored 8.0/10 in 4,243 reviews.

St. Charles

Chesterfield

Hermann

Fairview Heights

Maryland Heights

Florissant

O'Fallon

Fenton

Collinsville

Wentzville

Alton

St. Peters

Farmington

Festus

Glencoe

Clayton

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.

An easier way to manage your St. Louis trip

We make it super easy to schedule, organize and travel with friends or family. Trips is free — and available to use no matter where you book.

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Cheap flights from Ontario to St. Louis from $71

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 9/2. 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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Find the cheapest flights from Ontario to St. Louis (ONT-STL)

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Cheap one-way flights

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Frontier flights from Ontario to St. Louis

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

Alaska Airlines flights from Ontario to St. Louis

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

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Use the filters below to find and compare flights from Ontario to St. Louis that are best for you.

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?

What is the cheapest day to depart on your flight to St. Louis?

What is the cheapest time of day to depart on your flight to St. Louis?

How far in advance should I book a flight to St. Louis?

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

As of August 2025, prices for Ontario to St. Louis flights are approximately 7% cheaper when compared to flights at the same time last year.

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

Frontier, Hawaiian Airlines, and Alaska Airlines are the most popular carriers operating from Ontario to Lambert-St Louis

What airlines fly to St. Louis?

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

Denver (DEN) was the most common stop: 89% of momondo users choosing 1-stop flights on this route connected there.

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

Flights via Denver (DEN) offer the lowest average round-trip price of $279.

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

Flights connecting via Atlanta (ATL) have the shortest average one-way travel time: 6h 29m.

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

Atlanta (ATL) has the shortest average layover time for this route: 1h 05m.

How many flights depart from Ontario to St. Louis on average per week?

As of August 2025, 3 flights take off from Ontario and land in St. Louis each week. The most common flight departure day for this route is Mon, with 33% of weekly flights taking off on this day.

When to book flights from Ontario to St. Louis

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

Direct flights

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

When did momondo last update prices for flights from Ontario Airport to Lambert-St Louis Airport?

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?

What documentation or ID do you need to fly to Lambert-St Louis Airport?

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

Southwest Flights From Ontario to St. Louis

Traveling to a place near St. Louis?

Why use momondo?

Why should I use momondo to find a flight deal from Ontario to St. Louis?

Can I find flights from Ontario to St. Louis with flexible booking policies on momondo?

How can momondo help me find flights from Ontario to St. Louis?

I’m not ready to book a flight from Ontario to St. Louis right now. Can momondo alert me if prices change?

An easier way to manage your St. Louis trip

We make it super easy to schedule, organize and travel with friends or family. Trips is free — and available to use no matter where you book.

Get notified when prices go down

Daily price changes in your inbox - only with Price Alerts.

Find better results for your trip to the United States

Airports servicing Missouri