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 connection time from Ontario to St. Louis?

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

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

Phoenix (PHX) was the most common stop: 67% of momondo users choosing 1-stop flights on this route connected there.

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.

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 53% of people opting to fly with this airline when traveling to St. Louis. Keep in mind that there are 7 different airlines that fly to St. Louis on a routine basis, so you have a few additional options to choose from.

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

Flights via Denver (DEN) offer the lowest average round-trip price of $165.

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 July 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.

$71 Cheap Flights from Ontario to St. Louis in 2026

Discover deals from 900+ travel sites with momondo.

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.

6:15 am - 7:17 pm

ONT

STL

11h 02m

1 stop

8:10 pm - 10:30 am

STL

ONT

16h 20m

1 stop

$140Frontier

Wed, Sep 9 - Wed, Sep 16

6:15 am - 7:17 pm

ONT

STL

11h 02m

1 stop

8:10 pm - 10:30 am

STL

ONT

16h 20m

1 stop

$172Frontier

Mon, Sep 21 - Mon, Sep 28

7:12 am - 5:10 pm

ONT

STL

7h 58m

1 stop

7:58 pm - 11:50 pm

STL

ONT

5h 52m

1 stop

$308Multiple Airlines

Mon, Aug 24 - Mon, Aug 24

12:04 pm - 11:59 pm

ONT

STL

9h 55m

1 stop

6:45 pm - 4:22 pm

STL

ONT

23h 37m

1 stop

$313Multiple Airlines

Tue, Aug 18 - Wed, Aug 19

5:05 pm - 12:41 am

ONT

STL

5h 36m

1 stop

8:00 am - 12:16 pm

STL

ONT

6h 16m

1 stop

$367Delta

Tue, Aug 18 - Sat, Aug 29

1:06 pm - 9:00 pm

ONT

STL

5h 54m

1 stop

5:00 pm - 10:23 pm

STL

ONT

7h 23m

1 stop

$367Delta

Sat, Aug 22 - Sat, Aug 29

1:04 pm - 8:52 pm

ONT

STL

5h 48m

1 stop

10:14 am - 6:17 pm

STL

ONT

10h 03m

2 stops

$372American Airlines

Wed, Sep 16 - Sat, Sep 26

12:59 pm - 12:14 am

ONT

STL

9h 15m

2 stops

5:42 am - 11:43 am

STL

ONT

8h 01m

1 stop

$372American Airlines

Thu, Aug 20 - Thu, Aug 27

9:15 am - 6:04 pm

ONT

STL

6h 49m

1 stop

1:36 pm - 8:01 pm

STL

ONT

8h 25m

2 stops

$372United Airlines

Tue, Aug 18 - Wed, Aug 19

9:01 am - 8:46 pm

ONT

STL

9h 45m

2 stops

1:36 pm - 8:01 pm

STL

ONT

8h 25m

2 stops

$378United Airlines

Mon, Aug 24 - Tue, Aug 25

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Frontier flights from Ontario to St. Louis

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

Frontier

Sep 9

ONT6:15 amOntario

11h 02m

1 stop

STL7:17 pmLambert-St Louis

Sep 16

STL8:10 pmLambert-St Louis

16h 20m

1 stop

ONT10:30 amOntario

$140

Frontier

Sep 21

ONT6:15 amOntario

11h 02m

1 stop

STL7:17 pmLambert-St Louis

Sep 28

STL8:10 pmLambert-St Louis

16h 20m

1 stop

ONT10:30 amOntario

$172

Frontier

Sep 3

ONT10:49 amOntario

6h 24m

1 stop

STL7:13 pmLambert-St Louis

Sep 9

STL8:10 pmLambert-St Louis

16h 20m

1 stop

ONT10:30 amOntario

$195

Fly from

Fly to

Route

Depart

Return

Price

Cheapest round-trip

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 9/9

6:15 am-7:17 pm

1 stop11h 02m

Lambert-St Louis

Wed 9/16

8:10 pm-10:30 am

1 stop16h 20m

$140

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 9/21

6:15 am-7:17 pm

1 stop11h 02m

Lambert-St Louis

Mon 9/28

8:10 pm-10:30 am

1 stop16h 20m

$172

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 8/24

7:12 am-5:10 pm

1 stop7h 58m

Lambert-St Louis

Mon 8/24

7:58 pm-11:50 pm

1 stop5h 52m

$308

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/18

12:04 pm-11:59 pm

1 stop9h 55m

Lambert-St Louis

Wed 8/19

6:45 pm-4:22 pm

1 stop23h 37m

$313

Quickest round-trip

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/18

5:05 pm-12:41 am

1 stop5h 36m

Lambert-St Louis

Sat 8/29

8:00 am-12:16 pm

1 stop6h 16m

$367

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 8/22

1:06 pm-9:00 pm

1 stop5h 54m

Lambert-St Louis

Sat 8/29

5:00 pm-10:23 pm

1 stop7h 23m

$367

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 9/16

1:04 pm-8:52 pm

1 stop5h 48m

Lambert-St Louis

Sat 9/26

10:14 am-6:17 pm

2 stops10h 03m

$372

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 8/20

12:59 pm-12:14 am

2 stops9h 15m

Lambert-St Louis

Thu 8/27

5:42 am-11:43 am

1 stop8h 01m

$372

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/18

9:15 am-6:04 pm

1 stop6h 49m

Lambert-St Louis

Wed 8/19

1:36 pm-8:01 pm

2 stops8h 25m

$372

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 8/24

9:01 am-8:46 pm

2 stops9h 45m

Lambert-St Louis

Tue 8/25

1:36 pm-8:01 pm

2 stops8h 25m

$378

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 typical price of a round-trip flight between Ontario and St. Louis?

Prices are currently low for flights on this route.

Typical prices usually range from $268 to $403.
The lowest price recently found on this route was $140.

What is the cheapest month to fly to St. Louis?

In general, April 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 $250. The month of September is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $262.

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 $415. 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 $566. 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 $331 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 $571 per ticket.

How far in advance should I book a flight from Ontario 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 $362 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 $318 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 19m
Direct flights	None

The fastest flight from Ontario to St. Louis takes 5h 19m

There are no direct flights from Ontario to St. Louis. There are no popular flight routes from Ontario to St. Louis.

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Frequently asked questions about flying from Ontario to St. Louis

How far is Ontario to Lambert-St Louis by plane?
There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 19m 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 July 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 49% of all bookings. The subsequent popular airlines are Southwest at 21%, American Airlines at 20%, and United Airlines at 6%.

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 $105	Free Cancellation	Rating 5.6 2,749 reviews	Search Frontier flights
Delta	PriceFrom $165	Free Cancellation	Rating 7.8 8,485 reviews	Search Delta flights
United Airlines	PriceFrom $292	Free Cancellation	Rating 7.4 10,052 reviews	Search United Airlines flights
American Airlines	PriceFrom $292	Free Cancellation	Rating 7.1 11,839 reviews	Search American Airlines flights
Southwest	PriceFrom $316	Free Cancellation	Rating 8.0 4,228 reviews	Search Southwest flights

St. Charles

Chesterfield

Fairview Heights

Hermann

St. Peters

Maryland Heights

Florissant

Collinsville

O'Fallon

Alton

Fenton

Farmington

Clayton

Wentzville

Festus

Eureka

Litchfield

Edwardsville

Grafton

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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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 10/20. 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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Frontier flights from Ontario to St. Louis

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How to get the cheapest flight ticket from Ontario to St. Louis

What is the typical price of a round-trip flight between Ontario and St. Louis?

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 from Ontario to St. Louis?

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

What is the cheapest airline that flies 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?

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

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

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

When to book flights from Ontario to St. Louis

Cheap Ontario to St. Louis (ONT to STL) flight deals and tips

Fastest flight time

Direct flights

Frequently asked questions about flying 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

Traveling to a place near St. Louis?

Why use momondo?

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

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Airlines are sorted and displayed according to clicks in the past 7 days on momondo

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List of cabin classes available on flights landing in St. Louis. Availability may vary depending on flight origin and airline.

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