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 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 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 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

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.

2:08 pm - 1:09 pm

ONT

STL

21h 01m

1 stop

2:51 pm - 7:59 am

STL

ONT

19h 08m

1 stop

$152Frontier

Thu, Feb 26 - Sat, Feb 28

3:07 pm - 9:06 pm

ONT

STL

27h 59m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$159Frontier

Wed, Feb 4 - Sat, Feb 7

3:07 pm - 9:06 pm

ONT

STL

27h 59m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$160Frontier

Wed, Feb 4 - Sat, Feb 7

6:00 am - 1:56 pm

ONT

STL

5h 56m

1 stop

2:51 pm - 11:59 pm

STL

ONT

11h 08m

1 stop

$164Frontier

Sat, Feb 14 - Sat, Feb 21

7:17 pm - 9:26 pm

ONT

STL

24h 09m

1 stop

4:51 pm - 9:34 pm

STL

ONT

6h 43m

1 stop

$165Frontier

Wed, Feb 11 - 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

$170Frontier

Wed, Feb 25 - Sat, Feb 28

3:07 pm - 9:06 pm

ONT

STL

27h 59m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$171Frontier

Wed, Jan 28 - Sat, Jan 31

2:08 pm - 9:49 am

ONT

STL

17h 41m

1 stop

8:12 pm - 10:59 pm

STL

ONT

28h 47m

1 stop

$177Frontier

Thu, Mar 5 - Sat, Mar 7

7:17 pm - 9:26 pm

ONT

STL

24h 09m

1 stop

1:59 pm - 11:59 pm

STL

ONT

12h 00m

1 stop

$180Frontier

Wed, Feb 18 - Fri, Feb 20

3:07 pm - 9:06 pm

ONT

STL

27h 59m

1 stop

3:46 pm - 11:24 pm

STL

ONT

9h 38m

1 stop

$181Frontier

Wed, Jan 28 - Sat, Jan 31

Frontier flights from Ontario to St. Louis

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

Frontier

Feb 26

ONT2:08 pmOntario

21h 01m

1 stop

STL1:09 pmLambert-St Louis

Feb 28

STL2:51 pmLambert-St Louis

19h 08m

1 stop

ONT7:59 amOntario

$152

Frontier

Feb 4

ONT3:07 pmOntario

27h 59m

1 stop

STL9:06 pmLambert-St Louis

Feb 7

STL3:46 pmLambert-St Louis

9h 38m

1 stop

ONT11:24 pmOntario

$159

Frontier

Feb 4

ONT3:07 pmOntario

27h 59m

1 stop

STL9:06 pmLambert-St Louis

Feb 7

STL3:46 pmLambert-St Louis

9h 38m

1 stop

ONT11:24 pmOntario

$160

Delta flights from Ontario to St. Louis

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

Delta

Feb 14

ONT1:15 pmOntario

8h 21m

1 stop

STL11:36 pmLambert-St Louis

Feb 24

STL7:00 amLambert-St Louis

7h 07m

1 stop

ONT12:07 pmOntario

$277

Delta

Feb 20

ONT5:00 pmOntario

5h 25m

1 stop

STL12:25 amLambert-St Louis

Feb 24

STL6:00 amLambert-St Louis

8h 02m

1 stop

ONT12:02 pmOntario

$285

Delta

Jan 27

ONT12:41 pmOntario

8h 56m

1 stop

STL11:37 pmLambert-St Louis

Jan 31

STL6:40 amLambert-St Louis

7h 36m

1 stop

ONT12:16 pmOntario

$577

Fly from

Fly to

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 2/26

2:08 pm-1:09 pm

1 stop21h 01m

Lambert-St Louis

Sat 2/28

2:51 pm-7:59 am

1 stop19h 08m

$152

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sat 2/7

3:46 pm-11:24 pm

1 stop9h 38m

$159

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/4

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sat 2/7

3:46 pm-11:24 pm

1 stop9h 38m

$160

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-11:59 pm

1 stop11h 08m

$164

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/11

7:17 pm-9:26 pm

1 stop24h 09m

Lambert-St Louis

Wed 2/18

4:51 pm-9:34 pm

1 stop6h 43m

$165

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

$170

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/28

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sat 1/31

3:46 pm-11:24 pm

1 stop9h 38m

$171

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 3/5

2:08 pm-9:49 am

1 stop17h 41m

Lambert-St Louis

Sat 3/7

8:12 pm-10:59 pm

1 stop28h 47m

$177

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 2/18

7:17 pm-9:26 pm

1 stop24h 09m

Lambert-St Louis

Fri 2/20

1:59 pm-11:59 pm

1 stop12h 00m

$180

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 1/28

3:07 pm-9:06 pm

1 stop27h 59m

Lambert-St Louis

Sat 1/31

3:46 pm-11:24 pm

1 stop9h 38m

$181

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 $389. 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. In the afternoon is when there is more demand to fly to St. Louis, so prices are often more expensive at around $409 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 $359 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 $279 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 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 $146	Free Cancellation	Rating 5.7 3,056 reviews	Search Frontier flights
Delta	PriceFrom $286	Free Cancellation	Rating 7.9 8,040 reviews	Search Delta flights
United Airlines	PriceFrom $292	Free Cancellation	Rating 7.4 9,156 reviews	Search United Airlines flights
American Airlines	PriceFrom $292	Free Cancellation	Rating 7.2 11,118 reviews	Search American Airlines flights
Southwest	PriceFrom $346	Free Cancellation	Rating 8.0 4,257 reviews	Search Southwest flights

St. Charles

Chesterfield

Hermann

Fairview Heights

Florissant

Maryland Heights

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.