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$107+ 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 9/2. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — STL
Jun 17 — Jun 241
Tue 6/17
Tue 6/24
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 28 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 June 12, 2025.

Round-trip from

$234
(CheapOair)

One-way from

$107
(Trip.com)

Popular in

March

Cheapest in

August

Average price

$340
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. 16% potential increase in price ($69 potential increase over avg. RT price).
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Cheapest flight prices on average. 3% potential price decrease ($12 potential savings vs. average RT price).
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Average for round-trip flights in June 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 June 12, 2025.

This CheapOair deal was found by Cheapflights users on 6/10. 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 CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 8/2612:59 amONT - STL
1 stop6h 12mFrontier
Sun 8/317:54 pmSTL - ONT
1 stop14h 51mFrontier
Deal found 6/10$234
This Delta deal was found by Cheapflights users on 6/11. 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.
Mon 6/305:08 pmONT - STL
1 stop5h 35mDelta
Sat 7/56:00 amSTL - ONT
1 stop6h 38mDelta
Deal found 6/11$279
This Southwest deal was found by Cheapflights users on 6/9. 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.
Mon 6/305:25 pmONT - STL
1 stop5h 55mSouthwest
Mon 8/117:15 amSTL - ONT
2 stops7h 25mSouthwest
Deal found 6/9$333
This Alaska Airlines deal was found by Cheapflights users on 6/9. 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.
Wed 7/302:21 pmONT - STL
1 stop7h 38mAlaska Airlines
Wed 9/36:00 amSTL - ONT
1 stop10h 09mAlaska Airlines
Deal found 6/9$337
This American Airlines deal was found by Cheapflights users on 6/12. 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.
Fri 8/112:59 amONT - STL
1 stop6h 19mAmerican Airlines
Thu 8/145:15 amSTL - ONT
2 stops8h 17mAmerican Airlines
Deal found 6/12$343
This United Airlines deal was found by Cheapflights users on 6/11. 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.
Mon 6/306:39 pmONT - STL
1 stop8h 15mUnited Airlines
Wed 7/26:30 amSTL - ONT
1 stop7h 44mUnited Airlines
Deal found 6/11$399

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 June 12, 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

Tue 8/26

12:59 am-9:11 am

1 stop6h 12m

Lambert-St Louis

Sun 8/31

7:54 pm-8:45 am

1 stop14h 51m

$234

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 6/30

5:08 pm-12:43 am

1 stop5h 35m

Lambert-St Louis

Sat 7/5

6:00 am-10:38 am

1 stop6h 38m

$279

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 6/30

5:25 pm-1:20 am

1 stop5h 55m

Lambert-St Louis

Mon 8/11

7:15 am-12:40 pm

2 stops7h 25m

$333

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 7/30

2:21 pm-11:59 pm

1 stop7h 38m

Lambert-St Louis

Wed 9/3

6:00 am-2:09 pm

1 stop10h 09m

$337

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 8/1

12:59 am-9:18 am

1 stop6h 19m

Lambert-St Louis

Thu 8/14

5:15 am-11:32 am

2 stops8h 17m

$343

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 6/30

6:39 pm-4:54 am

1 stop8h 15m

Lambert-St Louis

Wed 7/2

6:30 am-12:14 pm

1 stop7h 44m

$399

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Tue 9/2

12:59 am-9:11 am

1 stop6h 12m

$107

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Fri 7/4

1:15 pm-9:38 pm

1 stop6h 23m

$140

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Mon 8/25

11:39 am-11:59 pm

1 stop10h 20m

$148

OntarioSt. Louis

ONT - STL

ONTSTL

Ontario

Wed 7/2

1:45 pm-9:45 pm

1 stop6h 00m

$170

Flights are sorted by cheapest round-trip flights first.

Deals found on 6/10

Showing 1-10 of 13 results
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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 June 9, 2025.

The best time to book flights from Ontario to St. Louis is 28 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 June 12, 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.

Rainfall in St. Louis by month

Plan your trip to St. Louis by taking into account the average rainfall totals by month.

In terms of precipitation, rainfall in St. Louis ranges from 2.2 - 4.7 inches per month. May is typically the wettest month, when rainfall can reach 4.7 in. February is typically the driest time to visit St. Louis when rainfall is around 2.2 in.

Temperature in St. Louis by month

Plan your trip to St. Louis by taking into account the average temperature totals by month.

If weather is an important factor for your trip to St. Louis, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 80.6 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 32.0 F).

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 June 12, 2025.
Read through reviews of airlines operating flights from Ontario to St. Louis, such as Alaska Airlines, Southwest and Delta. In addition to providing an overall rating, 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

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

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

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

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
4,287 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

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
7,950 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

Reviews

1 / 20
10.0
Excellent

James,Apr 2025

LAX - SFO

Good flight except the uncontrollable cold air from the ceiling.
Hawaiian Airlines
7.9
Good
2,494 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

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
8,790 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Food

7.1

Boarding

8.1

Comfort

7.8

Overall

8.0

Entertainment

7.1

Crew

8.5

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 Frontier is currently your cheapest option to St. Louis, with prices starting at $234. Additional round-trip tickets that might be worth considering are offered by Delta and Southwest, with the lowest prices starting at $279 and $333, respectively. Frontier is priced at 32% 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 ($107), Delta ($140), and Alaska Airlines ($148).

  • 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 Ontario?

Book flights to Ontario if you plan to visit one of these locations
O'Fallon
Maryland Heights
Fairview Heights
Collinsville
Eureka
St. Peters
Glencoe
Festus
Alton
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 June 12, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$130Average$211FlexibilityNo cancel feeOn-time62%
American AirlinesCheapest$306Average$422FlexibilityNo cancel feeOn-time71%
DeltaCheapest$311Average$410FlexibilityNo cancel feeOn-timeN/A
United AirlinesCheapest$316Average$429FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$340Average$416FlexibilityNo cancel feeOn-time63%

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