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$98+ Cheap flights from St. Louis to Ontario (STL - ONT)

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 8/27. Fares are subject to change and may not be available on all flights or dates of travel.
STL — ONT
Aug 3 — Aug 101
Sun 8/3
Sun 8/10
1 adult, Economy
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Cheapflights Tip: The best prices from Lambert-St Louis to Ontario are usually found in February or August, booked 77 days in advance, depart on a Tuesday or Wednesday and return on a Monday

Cheap flight deals from St. Louis to Ontario

Discover tips and strategies to find the most affordable flight options for your journey from St. Louis (STL) to Ontario (ONT). 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 29, 2025.

Round-trip from

$205
(Cheapflightsfares)

One-way from

$98
(Cheapflightsfares)

Popular in

March

Cheapest in

February

Average price

$381
From Lambert-St Louis to Ontario
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One-way flight from Lambert-St Louis to Ontario
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Highest demand for flights based on searches. 3% potential increase in price ($14 potential increase over avg. RT price).
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Cheapest flight prices on average. 5% potential price decrease ($20 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 St. Louis to Ontario

Cheapest flights from St. Louis to Ontario
Explore the most affordable flight options available from St. Louis to Ontario. Find the lowest fares from popular airlines and budget airlines, with prices last updated on July 29, 2025.

This Cheapflightsfares deal was found by Cheapflights users on 7/29. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 11/47:52 pmSTL - ONT
1 stop5h 58mFrontier
Fri 11/712:59 amONT - STL
1 stop6h 08mFrontier
Deal found 7/29$205
This American Airlines deal was found by Cheapflights users on 7/29. 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 8/307:53 amSTL - ONT
1 stop5h 39mAmerican Airlines
Sat 9/612:47 pmONT - STL
1 stop5h 28mAmerican Airlines
Deal found 7/29$277
This Hawaiian Airlines deal was found by Cheapflights users on 7/28. 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 Hawaiian Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 12/97:00 amSTL - ONT
1 stop10h 12mHawaiian Airlines
Sat 12/1311:30 amONT - STL
1 stop10h 26mHawaiian Airlines
Deal found 7/28$278
This Orbitz deal was found by Cheapflights users on 7/28. 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 Orbitz is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 8/266:00 amSTL - ONT
1 stop10h 09mMultiple Airlines
Mon 9/112:59 amONT - STL
1 stop6h 12mMultiple Airlines
Deal found 7/28$303
This Southwest deal was found by Cheapflights users on 7/28. 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.
Wed 8/2010:15 amSTL - ONT
2 stops9h 15mSouthwest
Tue 8/265:45 amONT - STL
2 stops9h 55mSouthwest
Deal found 7/28$319
This Alaska Airlines deal was found by Cheapflights users on 7/29. 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.
Thu 10/163:57 pmSTL - ONT
1 stop10h 06mAlaska Airlines
Tue 10/211:31 pmONT - STL
1 stop8h 32mAlaska Airlines
Deal found 7/29$331
This Delta deal was found by Cheapflights users on 7/27. 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 11/156:15 pmSTL - ONT
1 stop6h 31mDelta
Sat 1/311:56 amONT - STL
1 stop9h 43mDelta
Deal found 7/27$348
This United Airlines deal was found by Cheapflights users on 7/27. 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.
Sat 8/305:30 pmSTL - ONT
1 stop7h 00mUnited Airlines
Tue 9/27:00 amONT - STL
1 stop9h 23mUnited Airlines
Deal found 7/27$369

Cheapflights Fare Finder

 
Customize your flight search to find flights from St. Louis to Ontario 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 29, 2025.
Use the filters below to find and compare flights from St. Louis to Ontario that are best for you.

Fly from

St. Louis

Fly to

Ontario

Route

Depart

Return

Price

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 11/4

7:52 pm-11:50 pm

1 stop5h 58m

Ontario

Fri 11/7

12:59 am-9:07 am

1 stop6h 08m

$205

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 8/30

7:53 am-11:32 am

1 stop5h 39m

Ontario

Sat 9/6

12:47 pm-8:15 pm

1 stop5h 28m

$277

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 12/9

7:00 am-3:12 pm

1 stop10h 12m

Ontario

Sat 12/13

11:30 am-11:56 pm

1 stop10h 26m

$278

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Wed 8/20

7:11 pm-11:40 pm

1 stop6h 29m

Ontario

Tue 8/26

4:50 pm-12:38 am

1 stop5h 48m

$279

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 8/26

6:00 am-2:09 pm

1 stop10h 09m

Ontario

Mon 9/1

12:59 am-9:11 am

1 stop6h 12m

$303

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Wed 8/20

10:15 am-5:30 pm

2 stops9h 15m

Ontario

Tue 8/26

5:45 am-5:40 pm

2 stops9h 55m

$319

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Thu 10/16

3:57 pm-12:03 am

1 stop10h 06m

Ontario

Tue 10/21

1:31 pm-12:03 am

1 stop8h 32m

$331

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Sat 8/30

5:30 pm-10:30 pm

1 stop7h 00m

Ontario

Tue 9/2

7:00 am-6:23 pm

1 stop9h 23m

$369

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Wed 8/27

7:54 pm-11:50 pm

1 stop5h 56m

$98

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

Tue 12/9

2:55 pm-10:37 pm

1 stop9h 42m

$135

Flights are sorted by cheapest round-trip flights first.

Deals found on 7/28

Showing 1-10 of 14 results
1
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Best time to book a flight from St. Louis to Ontario

Have a flexible travel schedule? Discover the best time to fly to Ontario from St. Louis 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 St. Louis to Ontario

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

Use this chart to determine the optimal time to book a round-trip flight from St. Louis to Ontario. Price data was last updated on July 25, 2025.

The price you pay for your flight from St. Louis to Ontario may vary depending on when you book. For the best chance of a lower fare, look to book 66 days in advance of your trip. Fares are likely to increase a fortnight or so before your departure date.

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

Currently, August is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $246). Flying from St. Louis to Ontario in March is currently the most expensive (average of $328). 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 STL to ONT?

Find hourly flight availability from St. Louis to Ontario. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated July 29, 2025.

It’s optimal to fly from St. Louis to Ontario in the afternoon. By choosing this option you can save up to 19% on the cost of your flight, compared to a flight in the morning.

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

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

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

Reviews of airlines servicing Ontario

Get insights into the airlines that provide service to Ontario. 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 Ontario. Reviews last updated July 29, 2025.
Peruse reviews from past customers who have flown with Alaska Airlines, Southwest, and Delta from St. Louis to Ontario to help guide your decision. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.
Alaska Airlines
8.0
Very good
10,000 reviews

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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
4,238 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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
7,979 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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
2,605 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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
8,896 reviews
Alaska Airlines
8.0
Very good
10,000 reviews

Overall

8.0

Food

7.1

Crew

8.5

Comfort

7.8

Boarding

8.1

Entertainment

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 St. Louis to Ontario. 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 St. Louis to Ontario round-trip?

    Frontier, at $205, was found to be the cheapest airline from St. Louis to Ontario.Alternate airlines to your destination round-trip include American Airlines and Hawaiian Airlines. Frontier is priced at 43% lower than the current average price of a flight leaving 3 months from now.

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

    The cheapest airline one-way is Frontier, with whom users have recently found tickets for as low as $98. However, be on the lookout for offers from Alaska Airlines and American Airlines, as they are both options that can get you from St. Louis to Ontario for a low price.

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

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

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

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

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

    Yes. Cheapflights offers flight deals from St. Louis to Ontario 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 St. Louis to Ontario?

    Currently, August is the cheapest month in which you can book a flight from St. Louis to Ontario (average of $246). Flying from St. Louis to Ontario in March is currently the most expensive (average of $328). 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

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Alternative routes for St. Louis to Ontario

See prices for flight routes from nearby airports that may be better suited for you.
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Top 5 airlines flying from St. Louis to Ontario

Discover the top 5 airlines that operate flights from St. Louis to Ontario. 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 29, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$128Average$255FlexibilityNo cancel feeOn-time62%
DeltaCheapest$181Average$346FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$281Average$375FlexibilityNo cancel feeOn-time71%
SouthwestCheapest$341Average$416FlexibilityNo cancel feeOn-time63%
United AirlinesCheapest$344Average$416FlexibilityNo cancel feeOn-time69%

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