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$129+ 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 7/16. Fares are subject to change and may not be available on all flights or dates of travel.
STL — ONT
jun. 17 — jun. 241
mar. 6/17
mar. 6/24
1 adult, Economy
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Cheapflights Tip: The best prices from Lambert-St Louis to Ontario are usually found in February or June, 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 junio 12, 2025.

Round-trip from

$248
(Cheapflightsfares)

One-way from

$129
(Cheapflightsfares)

Popular in

March

Cheapest in

February

Average price

$281
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. 4% potential increase in price ($16 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 June 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 junio 12, 2025.

This Cheapflightsfares 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
vie. 8/297:54 pmSTL - ONT
1 stop5h 56mFrontier
dom. 8/3112:59 amONT - STL
1 stop6h 12mFrontier
Deal found 6/11$248
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.
lun. 8/45:23 pmSTL - ONT
1 stop7h 04mDelta
lun. 8/1110:00 pmONT - STL
1 stop8h 12mDelta
Deal found 6/11$297
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.
jue. 8/75:00 amSTL - ONT
2 stops9h 14mUnited Airlines
mar. 8/127:00 amONT - STL
1 stop6h 47mUnited Airlines
Deal found 6/11$302
This Alaska Airlines 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
mar. 12/97:00 amSTL - ONT
1 stop10h 12mAlaska Airlines
sáb. 12/136:00 amONT - STL
1 stop15h 56mAlaska Airlines
Deal found 6/10$305
This American 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 American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
mar. 12/95:26 amSTL - ONT
1 stop8h 04mAmerican Airlines
sáb. 12/136:47 amONT - STL
2 stops7h 20mAmerican Airlines
Deal found 6/11$311
This Southwest 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 Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
dom. 8/242:55 pmSTL - ONT
2 stops8h 55mSouthwest
dom. 8/317:50 amONT - STL
2 stops7h 50mSouthwest
Deal found 6/10$408

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 junio 12, 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

vie. 8/29

7:54 pm-11:50 pm

1 stop5h 56m

Ontario

dom. 8/31

12:59 am-9:11 am

1 stop6h 12m

$248

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

lun. 8/4

5:23 pm-10:27 pm

1 stop7h 04m

Ontario

lun. 8/11

10:00 pm-8:12 am

1 stop8h 12m

$297

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

jue. 8/7

5:00 am-12:14 pm

2 stops9h 14m

Ontario

mar. 8/12

7:00 am-3:47 pm

1 stop6h 47m

$302

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

mar. 12/9

7:00 am-3:12 pm

1 stop10h 12m

Ontario

sáb. 12/13

6:00 am-11:56 pm

1 stop15h 56m

$305

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

mar. 12/9

5:26 am-11:30 am

1 stop8h 04m

Ontario

sáb. 12/13

6:47 am-4:07 pm

2 stops7h 20m

$311

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

dom. 8/24

2:55 pm-9:50 pm

2 stops8h 55m

Ontario

dom. 8/31

7:50 am-5:40 pm

2 stops7h 50m

$408

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

mié. 7/16

7:29 pm-11:50 pm

1 stop6h 21m

$129

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

dom. 8/31

3:35 pm-11:59 pm

1 stop10h 24m

$139

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

mar. 7/1

7:15 pm-10:45 pm

1 stop5h 30m

$140

St. LouisOntario

STL - ONT

STLONT

Lambert-St Louis

dom. 11/2

4:01 pm-11:30 pm

1 stop9h 29m

$182

Flights are sorted by cheapest round-trip flights first.

Deals found on 6/9

Showing 1-10 of 13 results
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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 June 9, 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 junio 12, 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.

Rainfall in Ontario by month

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

In terms of precipitation, rainfall in Ontario ranges from 0.1 - 3.4 inches per month. February is typically the wettest month, when rainfall can reach 3.4 in. June is typically the driest time to visit Ontario when rainfall is around 0.1 in.

Temperature in Ontario by month

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

If weather is an important factor for your trip to Ontario, use this chart to help with planning. For those seeking warmer temperatures, August is the ideal time of year to visit, when temperatures reach an average of 78.8 F. Travelers looking to avoid the cold should look outside of December, when temperatures are typically at their lowest (around 53.6 F).

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 junio 12, 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. 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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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

Entertainment

7.1

Overall

8.0

Comfort

7.8

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 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 $248, was found to be the cheapest airline from St. Louis to Ontario.Alternate airlines to your destination round-trip include Delta and United Airlines. Frontier is priced at 31% 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 $129. However, be on the lookout for offers from Alaska Airlines and Delta, 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 junio 12, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$128Average$247FlexibilityNo cancel feeOn-time62%
DeltaCheapest$181Average$362FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$281Average$398FlexibilityNo cancel feeOn-time71%
United AirlinesCheapest$326Average$416FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$341Average$415FlexibilityNo cancel feeOn-time63%

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