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Cheap flights from Ontario to St. Louis from $88

1 adult
1 adult, Economy, 0 bags

Discover deals from 900+ travel sites with momondo.

Find the cheapest flights from Ontario to St. Louis

Cheap round-trip flights

Enter your travel dates to find the best prices.
Frontier Logo
11:30 am - 11:06 amONT  Ontario-STL Lambert-St Louis
21h 36m1 stop Denver Intl
Frontier Logo
7:58 pm - 10:45 amSTL  Lambert-St Louis-ONT Ontario
16h 47m1 stop Denver Intl
$199Frontier
Tue, Dec 1 - Fri, Dec 4
Frontier Logo
3:33 pm - 9:37 pmONT  Ontario-STL Lambert-St Louis
28h 04m1 stop Las Vegas Harry Reid Intl
Frontier Logo
7:02 pm - 12:05 amSTL  Lambert-St Louis-ONT Ontario
7h 03m1 stop Denver Intl
$227Frontier
Wed, Jan 6 - Wed, Jan 20
Multiple Airlines Logo
6:00 am - 11:04 amONT  Ontario-STL Lambert-St Louis
27h 04m1 stop Denver Intl
Multiple Airlines Logo
4:06 pm - 10:43 pmSTL  Lambert-St Louis-ONT Ontario
8h 37m1 stop Seattle/Tacoma Intl
$311Multiple Airlines
Tue, Dec 15 - Sat, Jan 16
Multiple Airlines Logo
6:00 am - 11:59 pmONT  Ontario-STL Lambert-St Louis
15h 59m1 stop Seattle/Tacoma Intl
Multiple Airlines Logo
7:54 pm - 10:45 amSTL  Lambert-St Louis-ONT Ontario
16h 51m1 stop Denver Intl
$340Multiple Airlines
Mon, Dec 7 - Mon, Dec 14
Delta Logo
1:07 pm - 11:26 pmONT  Ontario-STL Lambert-St Louis
8h 19m1 stop Atlanta Hartsfield-Jackson
Delta Logo
7:05 am - 12:12 pmSTL  Lambert-St Louis-ONT Ontario
7h 07m1 stop Salt Lake City
$431Delta
Wed, Jan 6 - Sat, Jan 9
Delta Logo
6:00 am - 1:26 pmONT  Ontario-STL Lambert-St Louis
5h 26m1 stop Salt Lake City
Delta Logo
7:05 am - 12:12 pmSTL  Lambert-St Louis-ONT Ontario
7h 07m1 stop Salt Lake City
$431Delta
Tue, Jan 5 - Sat, Jan 9
Southwest Logo
11:30 am - 8:15 pmONT  Ontario-STL Lambert-St Louis
6h 45m2 stops Phoenix Sky Harbor Intl Dallas Love Field
Southwest Logo
12:35 pm - 6:40 pmSTL  Lambert-St Louis-ONT Ontario
8h 05m2 stops Denver Intl Las Vegas Harry Reid Intl
$441Southwest
Wed, Jan 6 - Wed, Jan 20
American Airlines Logo
1:27 pm - 12:16 amONT  Ontario-STL Lambert-St Louis
8h 49m2 stops Phoenix Sky Harbor Intl Dallas/Fort Worth
American Airlines Logo
5:00 am - 9:44 amSTL  Lambert-St Louis-ONT Ontario
6h 44m1 stop Dallas/Fort Worth
$441American Airlines
Sat, Dec 26 - Thu, Dec 31
American Airlines Logo
6:00 am - 10:32 pmONT  Ontario-STL Lambert-St Louis
14h 32m1 stop Chicago O'Hare Intl
American Airlines Logo
6:57 pm - 11:59 pmSTL  Lambert-St Louis-ONT Ontario
7h 02m1 stop Dallas/Fort Worth
$485American Airlines
Tue, Dec 29 - Sun, Jan 3
Southwest Logo
5:55 am - 3:35 pmONT  Ontario-STL Lambert-St Louis
7h 40m2 stops Phoenix Sky Harbor Intl Dallas Love Field
Southwest Logo
8:25 am - 4:10 pmSTL  Lambert-St Louis-ONT Ontario
9h 45m2 stops Omaha Eppley Airfield Phoenix Sky Harbor Intl
$521Southwest
Fri, Dec 25 - Thu, Dec 31

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Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Dec 1
ONT11:30 amOntario
21h 36m
1 stop
STL11:06 amLambert-St Louis
Dec 4
STL7:58 pmLambert-St Louis
16h 47m
1 stop
ONT10:45 amOntario
$199
Frontier
Jan 6
ONT3:33 pmOntario
28h 04m
1 stop
STL9:37 pmLambert-St Louis
Jan 20
STL7:02 pmLambert-St Louis
7h 03m
1 stop
ONT12:05 amOntario
$227
Frontier
Dec 1
ONT11:30 amOntario
21h 36m
1 stop
STL11:06 amLambert-St Louis
Dec 2
STL7:58 pmLambert-St Louis
16h 47m
1 stop
ONT10:45 amOntario
$230

momondo Fare Finder

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

Fly from

Fly to

Route

Depart

Return

Price

Cheapest round-trip

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Tue 12/1

11:30 am-11:06 am

1 stop21h 36m

Lambert-St Louis

Fri 12/4

7:58 pm-10:45 am

1 stop16h 47m

$199

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Wed 1/6

3:33 pm-9:37 pm

1 stop28h 04m

Lambert-St Louis

Wed 1/20

7:02 pm-12:05 am

1 stop7h 03m

$227

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Tue 12/15

6:00 am-11:04 am

1 stop27h 04m

Lambert-St Louis

Sat 1/16

4:06 pm-10:43 pm

1 stop8h 37m

$311

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Mon 12/7

6:00 am-11:59 pm

1 stop15h 59m

Lambert-St Louis

Mon 12/14

7:54 pm-10:45 am

1 stop16h 51m

$340

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Wed 1/6

1:07 pm-11:26 pm

1 stop8h 19m

Lambert-St Louis

Sat 1/9

7:05 am-12:12 pm

1 stop7h 07m

$431
Quickest round-trip

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Tue 1/5

6:00 am-1:26 pm

1 stop5h 26m

Lambert-St Louis

Sat 1/9

7:05 am-12:12 pm

1 stop7h 07m

$431

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Wed 1/6

11:30 am-8:15 pm

2 stops6h 45m

Lambert-St Louis

Wed 1/20

12:35 pm-6:40 pm

2 stops8h 05m

$441

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Sat 12/26

1:27 pm-12:16 am

2 stops8h 49m

Lambert-St Louis

Thu 12/31

5:00 am-9:44 am

1 stop6h 44m

$441

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Tue 12/29

6:00 am-10:32 pm

1 stop14h 32m

Lambert-St Louis

Sun 1/3

6:57 pm-11:59 pm

1 stop7h 02m

$485

OntarioSt. Louis

ONT Ontario - STL Lambert-St Louis

ONTSTL

Ontario

Fri 12/25

5:55 am-3:35 pm

2 stops7h 40m

Lambert-St Louis

Thu 12/31

8:25 am-4:10 pm

2 stops9h 45m

$521

Flights are sorted by cheapest round-trip flights first.

Showing 1-10 of 20 resultsSorted by cheapest first
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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 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 $348 to $758.
The lowest price recently found on this route was $199.

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 May is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $325.

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 Wednesday when prices can be found for as low as $436. 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 $648. 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 $424 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 $597 per ticket.

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

As of November 2026, prices for Ontario to St. Louis flights are approximately 76% more expensive 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

Best Price Found

$88

Fastest flight time

5h 23m

Direct flights

None
The best one-way flight to St. Louis from Ontario in the past 72 hours is $88. The best round-trip flight deal from Ontario to St. Louis found on momondo in the last 72 hours is $199.
The fastest flight from Ontario to St. Louis takes 5h 23m
There are no direct flights from Ontario to St. Louis. There are no popular flight routes from Ontario to St. Louis.
Search flight deals

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 23m 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?

  • 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?

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
FrontierPriceFrom $165Free CancellationRating
5.5
2,505 reviews
Search Frontier flights
DeltaPriceFrom $165Free CancellationRating
7.8
8,719 reviews
Search Delta flights
American AirlinesPriceFrom $292Free CancellationRating
7.0
12,235 reviews
Search American Airlines flights
United AirlinesPriceFrom $325Free CancellationRating
7.3
10,492 reviews
Search United Airlines flights
SouthwestPriceFrom $348Free CancellationRating
8.0
4,219 reviews
Search Southwest flights

Traveling to a place near St. Louis?

Book flights to St. Louis if you plan to visit one of these locations
St. Charles
Chesterfield
Fairview Heights
Maryland Heights
St. Peters
Alton
Collinsville
Farmington
Florissant
Festus
Clayton
Hermann
Fenton
Edwardsville
O'Fallon
Eureka
Wentzville
Litchfield
Waterloo
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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