STL - ONT

$122 Find Cheap Flights from St. Louis to Ontario - Compare and Save

This is the cheapest one-way flight price found by a KAYAK user in the last 72 hours by searching for a flight from St. Louis to Ontario departing on 8/5. Fares are subject to change and may not be available on all flights or dates of travel. Click the price to replicate the search for this deal.
1 adult
1 adult, Economy, 0 bags

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Everything you should know

Cheapest round-trip
$224
Typical prices: $252-$315
Frontier
Tue 8/11Tue 8/18
STL - ONT • 1 stop
Cheapest one-way
$122
Typical prices: $119-$259
Frontier
Wed 8/5
STL - ONT • 1 stop
Nonstop flights
Not available
There are currently no direct flights between St. Louis and Ontario. You'll need at least 1 connection.
Insights
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Top layover airports
Cheapest • Avg $359 (round-trip)
Shortest trip • 5h 45m (one-way)
Insights
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When to travel
Cheapest • 22% price drop
Most popular
Good to know
Good to know
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Flight Deals
Booking Insights
Flight Deals

Cheap Flights from St. Louis to Ontario (STL-ONT)

 
Here are some of the best deals found on KAYAK recently from the most popular airlines for round-trip flights from St. Louis to Ontario that are departing in the next months. While these flights were available on KAYAK in the last 72 hours, prices and availability are subject to change and deals may expire.
Discover the best prices for you by selecting your travel dates on KAYAK.

Recent round-trip flight deals from St. Louis to Ontario

Tue, Aug 11 - Tue, Aug 18
Frontier Logo
8:08 pm - 11:50 pm
STL
-
ONT
29h 42m
1 stop
Frontier Logo
3:40 pm - 5:50 pm
ONT
-
STL
24h 10m
1 stop
$224Frontier
Tue, Aug 18 - Tue, Aug 25
Frontier Logo
8:00 am - 3:54 pm
STL
-
ONT
9h 54m
1 stop
Frontier Logo
3:40 pm - 5:50 pm
ONT
-
STL
24h 10m
1 stop
$230Frontier
Tue, Aug 18 - Tue, Aug 25
Frontier Logo
6:45 pm - 2:03 pm
STL
-
ONT
21h 18m
2 stops
Frontier Logo
3:40 pm - 5:50 pm
ONT
-
STL
24h 10m
1 stop
$235Frontier
Wed, Oct 21 - Sat, Oct 24
Frontier Logo
8:10 pm - 11:55 pm
STL
-
ONT
5h 45m
1 stop
Frontier Logo
11:16 am - 1:17 am
ONT
-
STL
12h 01m
1 stop
$248Frontier
Thu, Oct 15 - Tue, Oct 20
Frontier Logo
5:19 pm - 4:10 pm
STL
-
ONT
24h 51m
1 stop
Frontier Logo
11:16 am - 1:17 am
ONT
-
STL
12h 01m
1 stop
$251Frontier
Sat, Aug 1 - Sat, Aug 8
Frontier Logo
7:10 pm - 8:03 am
STL
-
ONT
14h 53m
1 stop
Frontier Logo
10:49 am - 7:23 pm
ONT
-
STL
6h 34m
1 stop
$254Frontier
Wed, Jul 22 - Tue, Jul 28
Frontier Logo
8:08 pm - 11:50 pm
STL
-
ONT
5h 42m
1 stop
Frontier Logo
10:49 am - 7:23 pm
ONT
-
STL
6h 34m
1 stop
$256Frontier
Wed, Aug 19 - Wed, Aug 26
Frontier Logo
6:45 pm - 4:22 pm
STL
-
ONT
23h 37m
1 stop
Frontier Logo
7:56 pm - 7:13 pm
ONT
-
STL
21h 17m
1 stop
$258Frontier
Wed, Oct 7 - Sat, Oct 10
Frontier Logo
12:46 pm - 8:54 pm
STL
-
ONT
10h 08m
1 stop
Frontier Logo
11:16 am - 1:17 am
ONT
-
STL
12h 01m
1 stop
$260Frontier
Sat, Aug 8 - Tue, Aug 11
Frontier Logo
8:08 pm - 11:50 pm
STL
-
ONT
5h 42m
1 stop
Frontier Logo
6:00 am - 7:23 pm
ONT
-
STL
11h 23m
1 stop
$264Frontier
Booking Insights

KAYAK's insights & trends for St. Louis to Ontario flights

Get data-powered insights and trends into flights from St. Louis to Ontario to help you find the cheapest flights, the best time to fly and much more.

How much is a round-trip flight from St. Louis to Ontario?

This analysis is based on the cheapest round-trip price found on KAYAK in the last 12 months by searching for a flight from St. Louis to Ontario departing in August.

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

To calculate monthly average prices, KAYAK takes all prices for each month over the last year for round-trip flights from St. Louis to Ontario, removes the top 0.1% to account for outliers, and then takes the median of all values for each month.

The cheapest month for flights from St. Louis to Ontario is November, where tickets cost $292 (return) on average. On the other hand, the most expensive months are June and March, where the average cost of round-trip tickets is $526 and $436 respectively.

Good to know

Low seasonSeptember
Cheapest flight$122
Best time to beat the crowds but there is an average 16% increase in price.
Most popular time to fly with an average 5% increase in price.
Flight from St. Louis to Ontario

When to book flights from St. Louis to Ontario

Are your dates flexible? Find out the best times to travel from St. Louis to Ontario based on our flight data from the last year. Discover the cheapest month and even day to fly.
Estimated round-trip price
KAYAK looks at all historical flight data for each date to provide a predicted price for one-way trips or round-trips with a duration up to 40 days. While we try to provide actual minimum prices for each date, some prices are predictions and actual prices may differ.

FAQs for booking flights from St. Louis to Ontario

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

    In the last 5 days, the lowest price for a flight from St. Louis to Ontario was $122 for a one-way ticket and $224 for a round-trip.

  • Do I need a passport to fly between St. Louis and Ontario?

    No

  • Which airports will I be using when flying from St. Louis to Ontario?

    St. Louis and Ontario are both served by 1 main airport. You will leave St. Louis from Lambert-St Louis and will be arriving at Ontario.

  • Which aircraft models fly most regularly from St. Louis to Ontario?

    We unfortunately don’t have that data for this specific route.

  • Which airline alliances offer flights from St. Louis to Ontario?

    Star Alliance, and oneworld are the airline alliances operating flights between St. Louis and Ontario, with Star Alliance being the most commonly used for this route.

  • Which is the best airline for flights from St. Louis to Ontario, Southwest or United Airlines?

    The two airlines most popular with KAYAK users for flights from St. Louis to Ontario are Southwest and United Airlines. With an average price for the route of $439 and an overall rating of 7.9, Southwest is the most popular choice. United Airlines is also a great choice for the route, with an average price of $510 and an overall rating of 7.4.

  • How does KAYAK find such low prices on flights from St. Louis to Ontario?

    KAYAK is a travel search engine. That means we look across the web to find the best prices we can find for our users. With over 2 billion flight queries processed yearly, we are able to display a variety of prices and options on flights from St. Louis to Ontario.

  • How does KAYAK's flight Price Forecast tool help me choose the right time to buy my flight ticket from St. Louis to Ontario?

    KAYAK’s flight Price Forecast tool uses historical data to determine whether the price for a flight to Ontario from St. Louis is likely to change within 7 days, so travelers know whether to wait or book now.

  • What is the Hacker Fare option on flights from St. Louis to Ontario?

    Hacker Fares allow you to combine one-way tickets in order to save you money over a traditional round-trip ticket. You could then fly to Ontario with an airline and back to St. Louis with another airline. Booking your flights between St. Louis and ONT can sometimes prove cheaper using this method.

  • What is KAYAK's "flexible dates" feature and why should I care when looking for a flight from St. Louis to Ontario?

    Sometimes travel dates aren't set in stone. If your preferred travel dates have some wiggle room, flexible dates will show you all the options when flying to Ontario from St. Louis up to 3 days before/after your preferred dates. You can then pick the flights that suit you best.

Reviews of the top 4 airlines serving from St. Louis to Ontario

 
See real verified KAYAK customer reviews for airlines flying from St. Louis to Ontario. Airline scores are aggregated from all reviews left by passengers on KAYAK after flying with an airline. KAYAK doesn’t show reviews that are older than 5 years. Learn how KAYAK collects reviews.
Need help choosing which airline to fly with from St. Louis to Ontario? KAYAK airline reviews give an overall score for each airline based on loads of factors, including comfort, boarding, in-flight entertainment and more, to make your decision easier. See airline scores according to verified KAYAK customer reviews.
7.9
SouthwestOverall score based on 4250 reviews
8.0Comfort
7.0Food
8.1Boarding
8.6Crew
7.5Entertainment
Airline reviews

It was just okay, no frills, basic transportation with no luxury. No screens on the seats, no water or drinks on a short flight. Full flight but at least it was on time.

6.0 GoodSteven, Jun 2026
LAS - ONT
Read more Southwest reviews

It was just okay, no frills, basic transportation with no luxury. No screens on the seats, no water or drinks on a short flight. Full flight but at least it was on time.

Snacks are always pretzels. Why can't you also offer peanuts ?

Only downside was the legroom and seat width, which is always a problem unless I spend more for a premium seat.

Very good. Sad to learn Southwest is going start to charge for bags

Exceptional crew! Friendly and professional. Pleasant attitude and treated everyone with respect.

The flight was promptly on schedule and Southwest delivered everything they promised. No excuses for any shortfalls just 100% ownership of their responsibilities and business. The boarding and seating policy is a complete shambles. What started out as a great idea when Southwest first hit the market has been turned into a disaster due to the lack of integrity in many of the people who fly Southwest and take advantage of Southwest generosity at the expense of their fellow passengers.

Crew was excellent - Plane was fine. Media was good, could use more kid shows; Not a fan of the brownie brittle -- snack could be slightly better.

Our flight to Oakland was great bc the plane was new but it was delayed by 15min not bad at all. Over all it was an 8/10

Left on time and arrived early. Brand new plane and no parts missing. Comfortable seats. The actual Captain spoke prior to the flight and reassured everyone about safety. Crew was so nice and fun. Perfect flight!

The flight in it self was good. The delays looking for pilots was unexpected.

Know that the movies that you are going to be offered are the oldest be rated movies they could possibly get. They may have one or two new movies that they keep advertising but when you’re flying 15 hours, there is nothing to see past the first new movie.

This was an overnight flight, and in the morning they did know coffee service. How you can throw passengers in a San Francisco airport at 5:40 a.m. in the morning and not giving them Coffee is a crime.

Our flight was delayed several Times due to mechanical issues. Although I understand this may happen at times, it was very inconvenient and we had to book a hotel for an overnight stay. We were traveling with my 3-yo grandson and waiting at the airport from noon until 6:30pm with no reassurance that our next rescheduled flight would depart, we had to decide what’s best for him. A day later, I found out that I may be able to demand compensation if my flight is delayed more than 4 hours. I will hav to read the fine print next time.

Service was professional and quick. Premium economy seat was comfortable given the class

HORRIBLE, my initial flight was cancelled, they made me pay $200 extra dollars and that got cancelled as well! After 6 cancellations I decided to get a refund because I needed to get home to my babies. Out of $1000+ dollars they offered me only $40 in refund! Totally unacceptable! The flight that they cancelled I was able to fly it on another airline. I had to spend $400 on one way tickets just to get home! I’m still getting the runaround.

Flight was delayed only slightly before takeoff due to traffic control. However, the flight arrived early to ORD. Good flight. United has been very reliable for me.

Overall a very poor experience - booked premium economy tickets but due to last minute flight delays , all my itinery went for a toss and had to fly economy class with no access to lounge or any compensation by united airlines to make up for the flight delays . i had expected better experience than that from united.

Airline did not explain reasons why flight was delayed two hours. Explanations were badly needed and rarely provided. Problem seemed to clearly be the airline’s fault and not the fault of the weather or airport.

Onboarding - it would be great to see on the screen what group they were boarding. It was very confusing on who was boarding (even though they called it out) they were not clear and the space to board was strange.

Older plane. Food was really bad, almost not worth the effort. Huge difference with European based airlines.

American delayed the flight for a crew rest period. The delay occurred late in the evening - the earliest i can find is 10:20 pm. With a 6 am flight anyone on the flight would have already have been asleep (unless you are insane, a vampire or on drugs) and at least for me i was already on the way to the airport at 445 am the next morning when i discovered they delayed the flight until 9 am. Given the incoming flight was in the air at 6 pm the evening before this should have been figured out a lot more timely that was there only crew to use. Just frustrating given there is no consideration for customer experience anymore in flying.

Good crew and flight was on time. It’s a small plane with limited overhead luggage space. They said the overhead space was full and I had to check my bag. There was still space when I got on. Waiting for my checked luggage added 30 minutes to my trip. Not the end of the world but also not great.

Smooth flight. From the early boarding and all were on board before departure time and arrived early in ONT. Great crew. Thank you!!!!

Trip delayed for 2 hours because of rain. We boarded and have to get down the flight and reboard again.

No enough space plus only allowing one laggage instead of two like other airlines.

Qatar airways ,boarding arrangements at Hamid international airport could been better

Amazing I love American. I’ll never fly anyone else if I can help it.

Everything was great except for the wifi was junk. Crew was super friendly and helpful

Everything minus the seat, was okay. Not enough room. 15 hours in a small space was hard on my back. I'm still quite sore.

It was fine. I didn't love the food but it was at least a real attempt at serving a meal, unlike my earlier flight from Nashville to Dallas.

Our flight was canceled. I will never use Kayak nor Frontier for travel again. The entire experience was a headache.

Terrible. The canceled my entire flight when I requested a refund for a trip frontier canceled trip one way.

i was unable to check in the flight. refund requested

I think Frontier was very good at communication. Their app worked very well. Loading was great and the flight was nice and easy.

The crew was mostly okay. The flight attendant who answered our questions was curt and unhelpful unfortunately. He seemed upset and I understand having off days.

Flight was cancelled and was not able to get another flight thru Frontier. Per frontier a refund was issued but I do not see a refund on my Afirm account.

The agent at check-in was strident, unwelcoming, and condescending to customers ahead of me.

I have come to accept Frontier as an absolute no-frills airline, paying for everything I want. A 4.5-hour flight should provide me with a complimentary beverage—rather, $4.9x for a soda. Or a bottle of water ought to be extended at no cost. 4 beers are on the menu, but only 1 type of beer is available (at $9.95). Also, so many restrictions to using a voucher from Barclay‘s Credit Card. Finally, try to reach a live agent for Frontier- impossible!

Was charged 99 dollars for a bag despite agents previously telling me it would be ok. Customer service was unhelpful

I will like you ( Frontier Airlines) to fly into LAX instead of ONT because I live in LA and the subway takes me to my house in just 15 minutes

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

Information on your arrival and departure airports