Latest deals
Insights
When to book
FAQs
Reviews
Price Alerts

Cheap flights from Ontario to St. Louis from $68

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 1/9. Fares may change, and may not be available for all flights or travel dates. Click the price to refresh the search for this deal.
1 adult
0 bags

Discover deals from 900+ travel sites with momondo.

Save money when you book flights with momondo

Big names and deals

Big names and deals

Search 100s of travel sites to compare prices.

Filter for what you want

Filter for what you want

Free Wi-Fi? Stopover? Instantly customize your results.

Trusted and free

Trusted and free

We’re completely free to use - no hidden charges or fees.

Price Alerts

Price Alerts

Not ready to book? to track prices.
Search flight deals

Find the cheapest flights from Ontario to St. Louis

Cheap round-trip flights

Enter your travel dates to find the best prices.
Frontier Logo
6:15 am - 12:12 pmONT-STL
27h 57m1 stop
Frontier Logo
10:10 pm - 3:09 pmSTL-ONT
18h 59m1 stop
$182Frontier
Find Deal
Thu, Dec 11 - Mon, Jan 5
Frontier Logo
6:45 am - 10:02 amONT-STL
25h 17m1 stop
Frontier Logo
10:10 pm - 5:15 pmSTL-ONT
21h 05m1 stop
$183Frontier
Find Deal
Tue, Dec 23 - Sun, Dec 28
Frontier Logo
6:00 am - 9:25 pmONT-STL
13h 25m1 stop
Frontier Logo
10:10 pm - 5:15 pmSTL-ONT
21h 05m1 stop
$184Frontier
Find Deal
Sun, Dec 21 - Sun, Dec 28
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
1:16 pm - 9:17 pmSTL-ONT
10h 01m1 stop
$198Frontier
Find Deal
Fri, Dec 12 - Mon, Dec 15
Frontier Logo
6:15 am - 12:12 pmONT-STL
27h 57m1 stop
Frontier Logo
7:43 pm - 11:09 amSTL-ONT
17h 26m1 stop
$202Frontier
Find Deal
Sat, Dec 6 - Wed, Dec 10
Frontier Logo
6:15 am - 12:12 pmONT-STL
27h 57m1 stop
Frontier Logo
10:44 pm - 9:17 pmSTL-ONT
24h 33m1 stop
$207Frontier
Find Deal
Wed, Dec 10 - Sun, Dec 14
Frontier Logo
6:00 am - 9:25 pmONT-STL
13h 25m1 stop
Frontier Logo
10:10 pm - 5:15 pmSTL-ONT
21h 05m1 stop
$208Frontier
Find Deal
Fri, Dec 19 - Sun, Dec 21
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
10:44 pm - 9:17 pmSTL-ONT
24h 33m1 stop
$209Frontier
Find Deal
Fri, Dec 12 - Sun, Dec 14
Frontier Logo
10:18 pm - 12:12 pmONT-STL
11h 54m1 stop
Frontier Logo
12:37 pm - 4:20 pmSTL-ONT
5h 43m1 stop
$217Frontier
Find Deal
Thu, Jan 8 - Sun, Jan 11
Frontier Logo
3:20 pm - 10:14 amONT-STL
16h 54m1 stop
Frontier Logo
3:30 pm - 9:17 pmSTL-ONT
31h 47m2 stops
$219Frontier
Find Deal
Fri, Dec 12 - Mon, Dec 15

Frontier flights from Ontario to St. Louis

Our best Frontier deals on Ontario to St. Louis flight tickets
Frontier
Feb 3
ONT7:15 amOntario
29h 31m
1 stop
STL2:46 pmLambert-St Louis
Feb 6
STL7:39 pmLambert-St Louis
6h 41m
1 stop
ONT12:20 amOntario
$163
Find similar
Frontier
Dec 11
ONT6:15 amOntario
27h 57m
1 stop
STL12:12 pmLambert-St Louis
Jan 5
STL10:10 pmLambert-St Louis
18h 59m
1 stop
ONT3:09 pmOntario
$182
Find similar
Frontier
Dec 23
ONT6:45 amOntario
25h 17m
1 stop
STL10:02 amLambert-St Louis
Dec 28
STL10:10 pmLambert-St Louis
21h 05m
1 stop
ONT5:15 pmOntario
$183
Find similar

Alaska Airlines flights from Ontario to St. Louis

Our best Alaska Airlines deals on Ontario to St. Louis flight tickets
Alaska Airlines
Jan 14
ONT11:53 amOntario
24h 01m
1 stop
STL1:54 pmLambert-St Louis
Jan 20
STL2:50 pmLambert-St Louis
26h 18m
1 stop
ONT3:08 pmOntario
$374
Find similar
Alaska Airlines
Dec 18
ONT6:00 amOntario
15h 59m
1 stop
STL11:59 pmLambert-St Louis
Jan 6
STL7:00 amLambert-St Louis
19h 14m
1 stop
ONT12:14 amOntario
$417
Find similar
Alaska Airlines
Feb 20
ONT6:14 amOntario
29h 37m
1 stop
STL1:51 pmLambert-St Louis
Feb 22
STL3:19 pmLambert-St Louis
10h 13m
1 stop
ONT11:32 pmOntario
$423
Find similar

momondo Fare Finder

 
Customize your flight search to find flights from Ontario to St. Louis that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, momondo users made 832,500 searches. Data last updated November 26, 2025.
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

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 12/11

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Mon 1/5

10:10 pm-3:09 pm

1 stop18h 59m

$182

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 12/23

6:45 am-10:02 am

1 stop25h 17m

Lambert-St Louis

Sun 12/28

10:10 pm-5:15 pm

1 stop21h 05m

$183

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 12/21

6:00 am-9:25 pm

1 stop13h 25m

Lambert-St Louis

Sun 12/28

10:10 pm-5:15 pm

1 stop21h 05m

$184

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Mon 12/15

1:16 pm-9:17 pm

1 stop10h 01m

$198

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 12/6

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Wed 12/10

7:43 pm-11:09 am

1 stop17h 26m

$202

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 12/10

6:15 am-12:12 pm

1 stop27h 57m

Lambert-St Louis

Sun 12/14

10:44 pm-9:17 pm

1 stop24h 33m

$207

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/19

6:00 am-9:25 pm

1 stop13h 25m

Lambert-St Louis

Sun 12/21

10:10 pm-5:15 pm

1 stop21h 05m

$208

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Sun 12/14

10:44 pm-9:17 pm

1 stop24h 33m

$209

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 1/8

10:18 pm-12:12 pm

1 stop11h 54m

Lambert-St Louis

Sun 1/11

12:37 pm-4:20 pm

1 stop5h 43m

$217

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 12/12

3:20 pm-10:14 am

1 stop16h 54m

Lambert-St Louis

Mon 12/15

3:30 pm-9:17 pm

2 stops31h 47m

$219

Flights are sorted by cheapest round-trip flights first.

Showing 1-10 of 20 resultsSorted by cheapest first
1
2

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?

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 $212. The month of September is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $241.

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 $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 Monday because tickets tend to average around $431. 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 $375 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 $426 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 $348 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 $296 on momondo.

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

As of November 2025, prices for Ontario to St. Louis flights are approximately 142% 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

Fastest flight time

5h 11m

Direct flights

None
The fastest flight from Ontario to St. Louis takes 5h 11m
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 30m 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 $144Free CancellationRating
5.8
3,099 reviews
Search Frontier flights
DeltaPriceFrom $286Free CancellationRating
7.9
7,999 reviews
Search Delta flights
United AirlinesPriceFrom $292Free CancellationRating
7.4
9,046 reviews
Search United Airlines flights
American AirlinesPriceFrom $296Free CancellationRating
7.2
11,038 reviews
Search American Airlines flights
SouthwestPriceFrom $346Free CancellationRating
8.0
4,254 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
Hermann
Fairview Heights
Florissant
Maryland Heights
O'Fallon
Wentzville
Fenton
Collinsville
St. Peters
Alton
Farmington
Festus
Glencoe
Edwardsville
Clayton
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.
Start using Trips
Find my bookings

Get notified when prices go down

Daily price changes in your inbox - only with Price Alerts.
1 adult
Fri 12/26
Fri 1/2
By creating a price alert you accept our terms of use and privacy policy.

Find better results for your trip to the United States