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 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 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.

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.

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.

8:40 am - 3:53 pm

ONT

STL

5h 13m

1 stop

2:51 pm - 11:59 pm

STL

ONT

11h 08m

1 stop

$148Frontier

Wed, Feb 25 - Sat, Feb 28

8:40 am - 3:53 pm

ONT

STL

5h 13m

1 stop

5:18 pm - 9:34 pm

STL

ONT

6h 16m

1 stop

$149Frontier

Wed, Feb 25 - Wed, Mar 4

3:24 pm - 9:26 pm

ONT

STL

28h 02m

1 stop

1:54 pm - 11:59 pm

STL

ONT

12h 05m

1 stop

$179Frontier

Thu, Feb 19 - Mon, Feb 23

8:07 am - 9:26 pm

ONT

STL

11h 19m

1 stop

10:11 pm - 1:11 pm

STL

ONT

17h 00m

1 stop

$182Frontier

Fri, Feb 13 - Mon, Feb 16

11:44 am - 9:00 pm

ONT

STL

7h 16m

1 stop

8:12 pm - 11:55 pm

STL

ONT

5h 43m

1 stop

$210Frontier

Thu, Apr 16 - Mon, Apr 20

10:03 pm - 12:15 pm

ONT

STL

12h 12m

1 stop

8:12 pm - 11:59 pm

STL

ONT

29h 47m

1 stop

$217Frontier

Wed, Mar 18 - Mon, Mar 23

10:50 am - 9:17 pm

ONT

STL

8h 27m

1 stop

8:16 pm - 11:56 pm

STL

ONT

5h 40m

1 stop

$224Frontier

Thu, Apr 2 - Mon, Apr 13

7:22 pm - 11:19 am

ONT

STL

13h 57m

1 stop

8:06 pm - 1:28 pm

STL

ONT

19h 22m

1 stop

$225Frontier

Thu, Mar 5 - Tue, Mar 10

8:40 am - 3:53 pm

ONT

STL

29h 13m

1 stop

10:11 pm - 11:59 pm

STL

ONT

27h 48m

2 stops

$226Frontier

Tue, Mar 3 - Thu, Mar 5

3:24 pm - 11:19 am

ONT

STL

17h 55m

1 stop

12:14 pm - 1:28 pm

STL

ONT

27h 14m

1 stop

$229Frontier

Thu, Mar 5 - Mon, Mar 9

Delta flights from Ontario to St. Louis

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

Delta

Feb 24

ONT5:00 pmOntario

5h 25m

1 stop

STL12:25 amLambert-St Louis

Mar 1

STL6:40 pmLambert-St Louis

7h 09m

1 stop

ONT11:49 pmOntario

$285

Delta

Feb 20

ONT10:20 pmOntario

8h 46m

1 stop

STL9:06 amLambert-St Louis

Feb 22

STL7:00 amLambert-St Louis

7h 07m

1 stop

ONT12:07 pmOntario

$293

Delta

Feb 21

ONT6:00 amOntario

5h 32m

1 stop

STL1:32 pmLambert-St Louis

Feb 28

STL7:00 amLambert-St Louis

7h 07m

1 stop

ONT12:07 pmOntario

$295

Frontier flights from Ontario to St. Louis

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

Frontier

Feb 25

ONT8:40 amOntario

5h 13m

1 stop

STL3:53 pmLambert-St Louis

Feb 28

STL2:51 pmLambert-St Louis

11h 08m

1 stop

ONT11:59 pmOntario

$148

Frontier

Feb 25

ONT8:40 amOntario

5h 13m

1 stop

STL3:53 pmLambert-St Louis

Mar 4

STL5:18 pmLambert-St Louis

6h 16m

1 stop

ONT9:34 pmOntario

$149

Frontier

Feb 19

ONT3:24 pmOntario

28h 02m

1 stop

STL9:26 pmLambert-St Louis

Feb 23

STL1:54 pmLambert-St Louis

12h 05m

1 stop

ONT11:59 pmOntario

$179

Fly from

Fly to

Route

Depart

Return

Price

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

$148

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/25

8:40 am-3:53 pm

1 stop5h 13m

Lambert-St Louis

Wed 3/4

5:18 pm-9:34 pm

1 stop6h 16m

$149

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/19

3:24 pm-9:26 pm

1 stop28h 02m

Lambert-St Louis

Mon 2/23

1:54 pm-11:59 pm

1 stop12h 05m

$179

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 2/13

8:07 am-9:26 pm

1 stop11h 19m

Lambert-St Louis

Mon 2/16

10:11 pm-1:11 pm

1 stop17h 00m

$182

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/16

11:44 am-9:00 pm

1 stop7h 16m

Lambert-St Louis

Mon 4/20

8:12 pm-11:55 pm

1 stop5h 43m

$210

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 3/18

10:03 pm-12:15 pm

1 stop12h 12m

Lambert-St Louis

Mon 3/23

8:12 pm-11:59 pm

1 stop29h 47m

$217

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 4/2

10:50 am-9:17 pm

1 stop8h 27m

Lambert-St Louis

Mon 4/13

8:16 pm-11:56 pm

1 stop5h 40m

$224

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 3/5

7:22 pm-11:19 am

1 stop13h 57m

Lambert-St Louis

Tue 3/10

8:06 pm-1:28 pm

1 stop19h 22m

$225

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 3/3

8:40 am-3:53 pm

1 stop29h 13m

Lambert-St Louis

Thu 3/5

10:11 pm-11:59 pm

2 stops27h 48m

$226

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 3/5

3:24 pm-11:19 am

1 stop17h 55m

Lambert-St Louis

Mon 3/9

12:14 pm-1:28 pm

1 stop27h 14m

$229

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 $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 $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 $407 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 $294 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 13m
Direct flights	None

The fastest flight from Ontario to St. Louis takes 5h 13m

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 13m 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 21%, American Airlines at 19%, 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 5.7 3,056 reviews	Search Frontier flights
Delta	PriceFrom $139	Free Cancellation	Rating 7.9 8,124 reviews	Search Delta flights
United Airlines	PriceFrom $292	Free Cancellation	Rating 7.4 9,212 reviews	Search United Airlines flights
American Airlines	PriceFrom $292	Free Cancellation	Rating 7.2 11,201 reviews	Search American Airlines flights
Southwest	PriceFrom $340	Free Cancellation	Rating 8.0 4,267 reviews	Search Southwest flights

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Chesterfield

Hermann

Fairview Heights

Maryland Heights

Florissant

O'Fallon

Collinsville

Fenton

St. Peters

Wentzville

Alton

Farmington

Clayton

Edwardsville

Eureka

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.