ONT - STL

$107 Find Cheap Flights from Ontario to St. Louis

This is the cheapest one-way flight price found by a KAYAK user in the last 72 hours by searching for a flight from Ontario to St. Louis departing on 9/2. 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

KAYAK searches hundreds of travel sites at once for deals on flights to St. Louis

 
These are the airlines KAYAK users have selected most often from within our search results in flight searches from Ontario to St. Louis, as well as popular online travel agencies
These are the airlines KAYAK users have selected most often from within our search results in flight searches from Ontario to St. Louis, as well as popular online travel agencies
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Flights Deals

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

 
Here are some of the best deals found on KAYAK recently from the most popular airlines for round-trip flights from Ontario to St. Louis 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 Ontario to St. Louis

Tue, Aug 26 - Sun, Aug 31
Frontier Logo
12:59 am - 9:11 amONT-STL
6h 12m1 stop
Frontier Logo
7:54 pm - 8:45 amSTL-ONT
14h 51m1 stop
$234Frontier
Find Deal
Thu, Aug 14 - Mon, Aug 18
Frontier Logo
12:59 am - 9:11 amONT-STL
6h 12m1 stop
Frontier Logo
7:29 pm - 11:50 pmSTL-ONT
6h 21m1 stop
$245Frontier
Find Deal
Mon, Jun 30 - Sat, Jul 5
Delta Logo
5:08 pm - 12:43 amONT-STL
5h 35m1 stop
Delta Logo
6:00 am - 10:38 amSTL-ONT
6h 38m1 stop
$279Delta
Find Deal
Mon, Jun 30 - Mon, Aug 11
Delta Logo
10:05 pm - 9:15 amONT-STL
9h 10m1 stop
Delta Logo
7:11 pm - 11:40 pmSTL-ONT
6h 29m1 stop
$288Delta
Find Deal
Mon, Jun 30 - Mon, Aug 11
Southwest Logo
5:25 pm - 1:20 amONT-STL
5h 55m1 stop
Southwest Logo
7:15 am - 12:40 pmSTL-ONT
7h 25m2 stops
$333Southwest
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Fri, Aug 1 - Tue, Aug 5
American Airlines Logo
12:59 am - 9:18 amONT-STL
6h 19m1 stop
American Airlines Logo
5:30 am - 12:00 pmSTL-ONT
8h 30m2 stops
$343American Airlines
Find Deal
Mon, Jun 30 - Fri, Jul 11
Southwest Logo
5:05 pm - 1:55 amONT-STL
6h 50m1 stop
Southwest Logo
3:40 pm - 9:10 pmSTL-ONT
7h 30m2 stops
$383Southwest
Find Deal
Mon, Jun 30 - Wed, Jul 2
United Airlines Logo
6:39 pm - 4:54 amONT-STL
8h 15m1 stop
United Airlines Logo
6:30 am - 12:14 pmSTL-ONT
7h 44m1 stop
$399United Airlines
Find Deal
Fri, Jun 27 - Sat, Jul 5
American Airlines Logo
12:59 am - 9:02 amONT-STL
6h 03m1 stop
American Airlines Logo
5:30 am - 12:00 pmSTL-ONT
8h 30m2 stops
$403American Airlines
Find Deal
Fri, Jul 4 - Tue, Jul 8
United Airlines Logo
1:19 pm - 11:39 pmONT-STL
8h 20m2 stops
United Airlines Logo
6:00 am - 12:14 pmSTL-ONT
8h 14m1 stop
$424United Airlines
Find Deal
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KAYAK's insights & trends for Ontario to St. Louis flights

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

What’s the cheapest day of the week to fly from Ontario to St. Louis?

The average price of all round-trip flights from Ontario to St. Louis clicked on KAYAK for each day over the last 12 months.

For Ontario to St. Louis, Monday is the cheapest day to fly on average and Sunday is the most expensive. Flying from St. Louis back to Ontario, the best deals are generally found on Tuesday, with Sunday being the most expensive.

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

To calculate monthly average prices, KAYAK takes all prices for each month over the last year for round-trip flights from Ontario to St. Louis, 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 Ontario to St. Louis is August, where tickets cost $214 (return) on average. On the other hand, the most expensive months are March and July, where the average cost of round-trip tickets is $470 and $401 respectively.

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

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

To get a below average price on the flight from Ontario to St. Louis, you should book around 1 week before departure. For the absolute cheapest price, our data suggests you should book 5 weeks before departure.

Good to know

Low seasonJanuary
High seasonJuly
Cheapest flight$107
Best time to beat the crowds with an average 14% drop in price.
Most popular time to fly with an average 16% increase in price.
Flight from Ontario to St. Louis

When to book flights from Ontario to St. Louis

Are your dates flexible? Find out the best times to travel from Ontario to St. Louis 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 Ontario to St. Louis

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

    In the last 3 days, the lowest price for a flight from Ontario to St. Louis was $107 for a one-way ticket and $234 for a round-trip.

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

    No

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

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

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

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

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

    The two airlines most popular with KAYAK users for flights from Ontario to St. Louis are Southwest and Delta. With an average price for the route of $416 and an overall rating of 8.0, Southwest is the most popular choice. Delta is also a great choice for the route, with an average price of $410 and an overall rating of 8.0.

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

    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 Ontario to St. Louis.

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

    KAYAK’s flight Price Forecast tool uses historical data to determine whether the price for a flight to St. Louis from Ontario 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 Ontario to St. Louis?

    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 St. Louis with an airline and back to Ontario with another airline. Booking your flights between Ontario and STL 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 Ontario to St. Louis?

    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 St. Louis from Ontario up to 3 days before/after your preferred dates. You can then pick the flights that suit you best.

Top 5 airlines serving from Ontario to St. Louis

 
See real verified KAYAK customer reviews for airlines flying from Ontario to St. Louis. 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 Ontario to St. Louis? 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.
8.0
SouthwestOverall score based on 4287 reviews
8.0Comfort
7.1Food
7.6Entertainment
8.6Crew
8.2Boarding
Airline reviews

Flight crew and cabin crew were great. I had to rearrange flights because my original flight was 3hrs delayed for weather, the rub is the flight I moved to boarded on time then we sat at the gate for 2 hours because scheduling stole our first officer for another flight, TWICE. Then our actual FO was an hour delayed. To make it worse my original flight went from a 3 hour delay to departing 15min EARLY. Just poor scheduling operations all around.

6.0 GoodAnonymous, May 2025HOU - MCI
Read more Southwest reviews

Flight crew and cabin crew were great. I had to rearrange flights because my original flight was 3hrs delayed for weather, the rub is the flight I moved to boarded on time then we sat at the gate for 2 hours because scheduling stole our first officer for another flight, TWICE. Then our actual FO was an hour delayed. To make it worse my original flight went from a 3 hour delay to departing 15min EARLY. Just poor scheduling operations all around.

It was a perfect flight in all aspects! Both legs!

Great flight, 47 passengers on a 180 seat plane. Stewardess was pleasant and cheerful.

I liked the crew member who gave flight instructions on "in case of a problem:. The seats are so small that only a young teenager could sit in middle seat.

Great flight staff. Ease of boarding. Overall, very uneventful and easy trip.

Employees were kind and funny, as always! Flight was late but no announcements were made for people with tight connections to help them transition quickly. No service due to turbulence.

It was 2 hours 45 minutes late, for no apparently clear reason.

I recently flew Southwest from San Jose to Honolulu. I was very impressed with the flight crew, especially the flight attendant in charge of the front of the plane. She came through the aisle at least five times for drinks and water, and two times for snacks. I have not seen such service since I flew first class. Also, for the first time, they gave us the correct baggage claim number, and the luggage came out quickly. I can't wait for Southwest to have assigned seating! I absolutely hate the Cattle Call boarding procedure and the mad dash to get seats and overhead bins. However, the boarding was efficient.

Crew was great flight was great baggage claim was a failure. It took over 1 hour for bags to arrive. Poor communication poor effort when I spoke to the supervisor about the delay

Everything was great except the food. The pretzels are really crappy.

It would be nice if was given wires ear buds. Overall was a good experience was able to sleep on the plane

737-800 in first class was pretty dumpy. Seat had an uncomfortable angle, storage under the seat was blocked so even my very modest backpack didn't fit, power outlet was flaky. Weird tiny seat pockets that couldn't hold a gallon ziploc bag, emesis bag missing, etc. etc. No in-flight service due to turbulence. Crew was excellent, boarding was smooth despite a full flight.

Delta flight was on time, seats were comfortable, and crew was nice.

Thank you for not flipping the plane on the run way. You guys get a 5 star rating for the flight!!!

Boarding is, as it always is… horrible. Gate lice. Slow moving zones. Too many people with carry ons

It was terrible, if they ran flights on time it would make a big difference.

Delta seems to be improving in many areas, except they are super bad with the food available. Bring back normal food service on long flights.

I actually received a notification from kayak on email but not one by text from Delta when my departure gait changed and I almost missed my flight

New boarding doesn't make sense. Filling front first is slow.

Delta flight was great from the check in all the way to arrival. However, I had a very bad experience. I requested a wheelchair and the wheelchair employee that went to pick me up from the plane in Boston to bring me to the baggage claims told me I have to pay him. I was under the impression that it was a free service and I usually give tips but the person forced me to pay and since I said no because I was upset with his demand when my daughter walked in to pick me up he demanded payment from my daughter who paid him thinking maybe now it is a charged service.

it was so bad. I tried to board my flight from vancouver to saskatoon. And to my surprise they did not board me cause the flight was changed and no email was send to me. and on my boarding pass which i got from seattle says different flight. I did not knew anyone from Vancouver, air canada crew was rude, i asked for today flight but they were rude and i had early morning dental appointment in saskatoon. I was so much in pain and my whole day is wasted today. and i suffered alot. They did provide me hotel but they did not provide me any food. I am really really disappointed first time had so bad experience with air canada. I may think twice to book it again. If i can get any reply or any composition that would be great. Thanks

Very comfortable (upgraded to business class). The audio on my screen didn’t work, but I managed to play the audio through my phone while watching the screen.

I was supposed to be on business class at first class from Denver back to Miami due to weather changes. I missed my connection and it’s put on a flight to Fort Lauderdale. Instead of honoring my business class/1st class ticket, they put me in coach, but there were two first class seats open. I think it’s absolutely disgusting that I paid for first class $1300 ticket and they put me in economy and they had to open seats available and I have still not been refunded the difference. I ended up having to eat a snack box instead of the meal I was supposed to get and did not get home till 2 AM so I think that’s a little pathetic that I had to live off crackers for dinner And my poor dog ate some cheese and salami. Oh yes, apparently when they switched me to the new flight they forgot to mention I had a service dog

Boarding seemed to be organized bedlam. For what ever reason, preboarding took longer than 20 minutes. Made the plane 20 minutes late taking off. Luckily we arrived on time. Flight crew seemed very friendly. Only slight turbulence.

The personnel were professional and friendly. The Boeing 737 Max 9 is too claustrophobic and was very warm at both airport gates, and still warm in the air.

While the staff was pleasant and helpful, the following observations are for your awareness. There was some delay on the tarmac on take off and landing. The paid lunch/food offerings were limited. Entertainment was only available on WiFi at a cost.

get E+, a must for 5 hours flight if you are tall

The first flight was better in terms of the aircraft.

The gate was too far away for the connecting flight

Compared with other carriers business class for an overnight was not worth the extra expense.

Eventless. It was a good flight and good crew. Can’t complaint.

Very helpful ground crew after an earlier flight delay and being rebooked on a different flight.

The plane was late and then sat on the runway for almost 45 minutes before taking off.

We kept being told that the flight was full and that all overhead compartments were full and therefore had to check in our hand luggage. We were some of the last people to board and noticed that there was still sufficient space in the overhead compartments. We were obliged to check in hand luggage when there was space and so had to wait at luggage retrieval which took a while to then noticed damage to our luggage - not a great experience!

This was an overnight flight. There was no meal service in first class, just a simple snack basket was offered along with beverages. There should have been some type of continental breakfast prior to arrival in PHL. As an Executive Platinum American Airlines Advantage member, I received no name recognition from the first class flight attendant. When disembarking at PHL, the flight attendants were more interested in their cell phones than saying "thank you" to the passengers as they disembarked.

The flight was quick and to the point. The crew just did their job w/o excessive talking and everything was just perfect.

Awkward carry on process. Forced to check all carry on. No overhead space of worthiness. Left delayed, but made up the time. Crew was amicable.

Amazingly comfy flight - I had upgraded for a reasonable price and it was worth it. The food also was good.

Had to wait on pilot and crew to depart and had to wait to arrive at the gate because they only had 2 crews working. Delays, delays....Planes just keep getting smaller and tighter and they nickle and dime for everything. When will an airline actually wake up and make flying more enjoyable?

I paid for what I got which was cheap, I brought my own entertainment. I knew what to expect, so I could be prepared. If you’re flying economy, check in early like me. I have no problems with my flight, was on time, staff were friendly, and overall good experience.

I liked the turn-style feature at gate 209B at LAX. Very efficient process. The gate staff also made several, clearly directed announcements so I felt very informed.

The seats were awful, hard plastic covered in sheet vinyl. The airline tries to scam you into paying extra to get seat together when the flight wasn’t full. They were going to separate a family with young children but my wife who had a row to herself gave up her seat so the young mom could be with her young boys. I’m never giving this airline my money again.

It was a short flight so no food or entertainment….

Frontier had yet another flight cancellation. Have never made a complete round trip with this airline without at least one leg getting cancelled. Miserable flights - dirty, uncomfortable planes that apparently always have issues since I've had multiple delays and cancellations with them.

Flight was delayed 3 times, would have been nice to have received text message instead of email notifications. Frontier app wasn’t even updated accordingly, no gate number disclosed. No agent at front desk of gate to inform of delay. Very confused and left if the dark

They changed the timing , first delayed by 4 hours then went back to 40 mins late, we had to run back to airport to not miss our flight. This is ridiculous

No frills for sure. No gate announcements about flight delay, not even water to drink on the flight.

I loked walking out on the tarmac to board and no first class. I didn't like that they have no snacks or onboard wifi to bide your time.

It was a redeye flight, so every passenger just wanted to sleep, but through the entire flight, the flight crew made announcements over the loudspeaker at maximum volume every few minutes making sleep impossible. For example: it’s 2am, and the crew decides to give an extremely detailed announcement about snacks and beverages for sale. And 3am is the perfect time to wake up everyone with a lengthy announcement about how to get a coffee refill and how to take advantage of new offer from frontier for a credit card.

The takeoff was the smoothest I've ever experienced on any airline and this is the first time I've flown on frontier so this was an extremely pleasant surprise!

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