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$130+ Cheap flights from Ontario to St. Louis (ONT - STL)

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 9/23. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Jul 26 — Aug 21
Sat 7/26
Sat 8/2
1 adult, Economy
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Cheapflights Tip: The best prices from Ontario to Lambert-St Louis are usually found in August or September, booked 54 days in advance, depart on a Monday or Tuesday and return on a Tuesday

Cheap flight deals from Ontario to St. Louis

Discover tips and strategies to find the most affordable flight options for your journey from Ontario (ONT) to St. Louis (STL). Learn about various techniques such as flexible date searches, comparing prices across and setting up price alerts. Use these methods to find the cheapest flights available for your travel needs. Data last updated July 21, 2025.

Round-trip from

$279
(American Airlines)

One-way from

$130
(Trip.com)

Popular in

March

Cheapest in

August

Average price

$379
From Ontario to Lambert-St Louis
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One-way flight from Ontario to Lambert-St Louis
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Highest demand for flights based on searches. 15% potential increase in price ($63 potential increase over avg. RT price).
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Cheapest flight prices on average. 3% potential price decrease ($11 potential savings vs. average RT price).
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Average for round-trip flights in July 2025
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Find flight deals from Ontario to St. Louis

Cheapest flights from Ontario to St. Louis
Explore the most affordable flight options available from Ontario to St. Louis. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 21, 2025.

This American Airlines deal was found by Cheapflights users on 7/21. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 9/1310:53 amONT - STL
1 stop7h 22mAmerican Airlines
Wed 9/175:18 amSTL - ONT
1 stop6h 46mAmerican Airlines
Deal found 7/21$279
This Alaska Airlines deal was found by Cheapflights users on 7/20. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 9/226:00 amONT - STL
1 stop9h 34mAlaska Airlines
Sat 10/46:33 amSTL - ONT
1 stop8h 04mAlaska Airlines
Deal found 7/20$292
This Delta deal was found by Cheapflights users on 7/20. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 9/207:05 amONT - STL
1 stop7h 00mDelta
Mon 9/227:00 pmSTL - ONT
1 stop6h 42mDelta
Deal found 7/20$293
This Frontier deal was found by Cheapflights users on 7/21. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 8/1212:59 amONT - STL
1 stop6h 12mFrontier
Thu 8/217:54 pmSTL - ONT
1 stop5h 56mFrontier
Deal found 7/21$305
This United Airlines deal was found by Cheapflights users on 7/19. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 8/211:15 pmONT - STL
1 stop5h 31mUnited Airlines
Mon 8/251:39 pmSTL - ONT
1 stop5h 50mUnited Airlines
Deal found 7/19$307
This Southwest deal was found by Cheapflights users on 7/20. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 9/211:50 pmONT - STL
2 stops8h 35mSouthwest
Fri 9/261:15 pmSTL - ONT
1 stop6h 10mSouthwest
Deal found 7/20$382

Cheapflights 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, Cheapflights users made 2,558,603 searches. Data last updated July 21, 2025.
Use the filters below to find and compare flights from Ontario to St. Louis that are best for you.

Fly from

Ontario

Fly to

St. Louis

Route

Depart

Return

Price

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 9/13

6:10 am-3:09 pm

1 stop6h 59m

Lambert-St Louis

Wed 9/17

7:16 am-1:54 pm

1 stop8h 38m

$279

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 9/22

6:00 am-5:34 pm

1 stop9h 34m

Lambert-St Louis

Sat 9/27

3:35 pm-10:44 am

1 stop21h 09m

$292

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 9/20

7:05 am-4:05 pm

1 stop7h 00m

Lambert-St Louis

Mon 9/22

7:00 pm-11:42 pm

1 stop6h 42m

$293

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 8/12

12:59 am-9:11 am

1 stop6h 12m

Lambert-St Louis

Thu 8/21

7:54 pm-11:50 pm

1 stop5h 56m

$305

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Thu 8/21

1:15 pm-8:46 pm

1 stop5h 31m

Lambert-St Louis

Mon 8/25

1:39 pm-5:29 pm

1 stop5h 50m

$307

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sun 9/21

1:50 pm-12:25 am

2 stops8h 35m

Lambert-St Louis

Fri 9/26

1:15 pm-5:25 pm

1 stop6h 10m

$382

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 9/23

8:59 pm-9:06 am

1 stop10h 07m

$130

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 10/22

1:31 pm-12:03 am

1 stop8h 32m

$137

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 10/7

1:31 pm-12:03 am

1 stop8h 32m

$139

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Sat 9/13

6:00 am-1:33 pm

1 stop5h 33m

$140

Flights are sorted by cheapest round-trip flights first.

Deals found on 7/19

Showing 1-10 of 11 results
1
2

Best time to book a flight from Ontario to St. Louis

Have a flexible travel schedule? Discover the best time to fly to St. Louis from Ontario with our price prediction graph.
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.

Cheapflights Insights

Everything you need to know about your flight from Ontario to St. Louis

How far ahead should I book a flight from Ontario to St. Louis?

Use this chart to determine the optimal time to book a round-trip flight from Ontario to St. Louis. Price data was last updated on July 18, 2025.

The best time to book flights from Ontario to St. Louis is 54 days before your desired departure date. The cost of your flight will likely increase significantly if you book two weeks in advance of your flight.

What is the cheapest month to book a flight from Ontario to St. Louis?

Currently, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

What is the cheapest time of day to fly from ONT to STL?

Find hourly flight availability from Ontario to St. Louis. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated July 21, 2025.

A simple way to save on the total cost of your ticket is to fly from Ontario to St. Louis in the afternoon. If you’re flexible enough to do this you can expect to save up to 60% on your trip compared to booking a flight at noon.

What is the cheapest day to fly from Ontario to St. Louis?

Use this chart to determine the cheapest time to fly round-trip from Ontario to St. Louis. Price data was last updated on December 16, 2024.

Travelers seeking maximum savings on their Ontario to St. Louis flight should consider departing on Wednesday at noon when fares are most often at their lowest. Monday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.

Reviews of airlines servicing St. Louis

Get insights into the airlines that provide service to St. Louis. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to St. Louis. Reviews last updated July 21, 2025.
Get a feel of what it's like to fly with Alaska Airlines, Southwest, and Delta from Ontario to St. Louis by reading reviews from past customers. Users have also rated airlines in terms of entertainment options, comfort, food, crew/service, and boarding process.
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Alaska Airlines
8.0
Very good
10,000 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Southwest
8.0
Very good
4,233 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Delta
8.0
Very good
7,962 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Hawaiian Airlines
7.8
Good
2,589 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
United Airlines
7.4
Good
8,867 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Crew

8.5

Overall

8.0

Entertainment

7.1

Boarding

8.1

Comfort

7.8

Food

7.1

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.

Related info for your journey

Find useful and relevant information for your journey from Ontario to St. Louis. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • What are the cheapest airlines flying from Ontario to St. Louis round-trip?

    Flying on American Airlines is currently your cheapest option to St. Louis, with prices starting at $279. Additional round-trip tickets that might be worth considering are offered by Alaska Airlines and Delta, with the lowest prices starting at $292 and $293, respectively. American Airlines is priced at 20% lower than the current average price of a flight leaving 3 months from now.

  • What are the cheapest airlines to fly from Ontario to St. Louis one-way?

    The cheapest airlines for a one-way flight from Ontario to St. Louis are Frontier ($130), Alaska Airlines ($137), and Hawaiian Airlines ($139).

  • Can I find deals for flights from Ontario to St. Louis that include hotel bookings?

    Yes. In addition to deals on Ontario to St. Louis flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Ontario to St. Louis?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Ontario to St. Louis.

  • Can I find deals for business class flights from Ontario to St. Louis?

    Yes. Cheapflights offers flight deals from Ontario to St. Louis by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from Ontario to St. Louis?

    Currently, August is the cheapest month in which you can book a flight from Ontario to St. Louis (average of $311). Flying from Ontario to St. Louis in March is currently the most expensive (average of $356). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

See more FAQs

Traveling to a place near St. Louis?

Book flights to St. Louis if you plan to visit one of these locations
O'Fallon
Maryland Heights
Fairview Heights
Collinsville
Eureka
St. Peters
Glencoe
Alton
Festus
Chesterfield
Farmington

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Top 5 airlines flying from Ontario to St. Louis

Discover the top 5 airlines that operate flights from Ontario to St. Louis. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated July 21, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$133Average$219FlexibilityNo cancel feeOn-time62%
American AirlinesCheapest$306Average$400FlexibilityNo cancel feeOn-time71%
DeltaCheapest$306Average$409FlexibilityNo cancel feeOn-timeN/A
United AirlinesCheapest$316Average$451FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$340Average$414FlexibilityNo cancel feeOn-time63%

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