ONT - STL

$72 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 1/28. 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

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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Everything you should know

Cheapest round-trip
$139
Overall average: $342
Frontier
Thu 1/29Sun 2/1
ONT - STL • 1 stop
Cheapest one-way
$72
Typical prices: $161-$249
Frontier
Wed 1/28
ONT - STL • 1 stop
When to book
2 weeks
in advance
Our data shows that travelers who book at least 2 weeks in advance save around 32% compared to booking last minute.
Insights
Insights
Insights
Insights
When to travel
September
Cheapest • 33% price drop
July
Most popular
Good to know
Good to know
+1
+1
Good to know
Good to know
+1
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We hope you love your trip to St. Louis!
Flight Deals
Booking Insights
Flight 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

Thu, Jan 29 - Sun, Feb 1
Frontier Logo
11:04 am - 9:06 pm
ONT
-
STL
8h 02m1 stop
Frontier Logo
9:32 pm - 12:10 pm
STL
-
ONT
16h 38m1 stop
$139Frontier
Wed, Feb 25 - Sat, Feb 28
Frontier Logo
8:40 am - 3:53 pm
ONT
-
STL
5h 13m1 stop
Frontier Logo
2:51 pm - 11:59 pm
STL
-
ONT
11h 08m1 stop
$144Frontier
Fri, Feb 6 - Sun, Feb 8
Frontier Logo
6:20 am - 6:44 pm
ONT
-
STL
10h 24m1 stop
Frontier Logo
9:32 pm - 12:10 pm
STL
-
ONT
16h 38m1 stop
$145Frontier
Fri, Feb 6 - Sun, Feb 8
Frontier Logo
6:20 am - 6:44 pm
ONT
-
STL
10h 24m1 stop
Frontier Logo
9:32 pm - 7:10 pm
STL
-
ONT
23h 38m1 stop
$147Frontier
Wed, Jan 28 - Sat, Jan 31
Frontier Logo
7:15 am - 2:46 pm
ONT
-
STL
5h 31m1 stop
Frontier Logo
3:46 pm - 11:24 pm
STL
-
ONT
9h 38m1 stop
$148Frontier
Tue, Feb 10 - Mon, Feb 16
Frontier Logo
8:36 am - 1:58 pm
ONT
-
STL
27h 22m1 stop
Frontier Logo
1:54 pm - 11:59 pm
STL
-
ONT
12h 05m1 stop
$149Frontier
Tue, Mar 24 - Sat, Mar 28
Frontier Logo
4:49 pm - 11:19 am
ONT
-
STL
16h 30m1 stop
Frontier Logo
12:14 pm - 9:03 pm
STL
-
ONT
10h 49m1 stop
$151Frontier
Wed, Feb 4 - Sun, Feb 8
Frontier Logo
3:07 pm - 9:06 pm
ONT
-
STL
27h 59m1 stop
Frontier Logo
9:32 pm - 12:10 pm
STL
-
ONT
16h 38m1 stop
$152Frontier
Wed, Feb 4 - Mon, Feb 9
Frontier Logo
7:15 am - 2:46 pm
ONT
-
STL
5h 31m1 stop
Frontier Logo
1:40 pm - 12:20 am
STL
-
ONT
12h 40m1 stop
$164Frontier
Sat, Feb 21 - Wed, Feb 25
Frontier Logo
6:00 am - 1:56 pm
ONT
-
STL
5h 56m1 stop
Frontier Logo
4:51 pm - 9:34 pm
STL
-
ONT
6h 43m1 stop
$165Frontier
Booking Insights

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 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 September, where tickets cost $241 (return) on average. On the other hand, the most expensive months are March and December, where the average cost of round-trip tickets is $455 and $426 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 2 weeks before departure, which saves you about 32% compared to booking last minute. For the absolute cheapest price, our data suggests you should book 5 weeks before departure.

Good to know

Low seasonJanuary
Cheapest flight$72
Best time to beat the crowds with an average 5% drop in price.
Most popular time to fly with an average 5% 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 $72 for a one-way ticket and $139 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?

    Star Alliance, SkyTeam, and oneworld are the airline alliances operating flights between Ontario and St. Louis, with Star Alliance 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 $425 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 $401 and an overall rating of 7.9.

  • 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.

Reviews of the 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 4250 reviews
7.5Entertainment
8.6Crew
8.1Boarding
8.0Comfort
7.0Food
Airline reviews

The boarding and seat assignment system no longer works for me, but I know it is being replaced. Otherwise, I am good with the overall experience.

8.0 ExcellentRussell, Dec 2025
SAN - OAK
Read more Southwest reviews

The boarding and seat assignment system no longer works for me, but I know it is being replaced. Otherwise, I am good with the overall experience.

The lead steward kept singing about "San Francisco" and hotel California---more annoying than humorous....needs work. Flight was smooth and on time.

San Diego airport is brand new, spacious, airy and very smooth checkin at SW baggage drop.

Crew could have been friendlier, maybe I'm spoiled by SW crews. In flight wifi was good. Would be nice to have more food offerings on a 4 plus hour flight

Ever since Southwest starting charging for bags, passengers don't want to pay to check their bags, so the gate agents have to beg people to check their roller bags now because there's "not enough space". This was a terrible business move by Southwest.

Sacrament staff are always polite and helpful. Airport is easy to maneuver and boarding is straightforward.

Boarded on time but once we were ready for take off, the crew determined that, although every seat was taken, somehow someone was on the wrong flight. Delay, delay delay, announcements and ended up with one person checking EVERY ID against their passenger Manifest only to figure out it was a "clerical error." We departed 54 minutes late causing me to run in the St. Louis Airport to make my connection and lose the priority boarding spot I had paid for. Unnecessary delay.

Flight was delayed due to plane not passing inspection And one of the crew had to time out and we had to wait for another one A 3 hour delay

As always, the entire Southwest experience was wonderful, from online booking to flight to baggage retrieval. Very grateful.

The weather could have been better. There was a 40 minute ATC delay in SFO because of marine fog and a micro cell storm delayed landing and take-off at Nashville. The gate was changed 5 minutes from boarding from gate B3 to gate C23 at Nashville airport.

The flight was delayed for about 2 hrs. Other than it, it was good.

I am extremely disappointed that delta internal pilot manuals now refer to the Gulf of Mexico as the “gulf of America”. You can bow down to the Orange turd on your own. I will never fly delta again

No lunch on a x-country flight scheduled for 10:50 am departure, arrived 5+ hrs later. That requires a black box label before you pay for the tickets. Worst, when I checked in online, it's specifically said that lunch was served on his flight for economy Plus passengers.

Our flight from SFO to MSP was right on time on 11/15/2025. No delays. As we approached MSP at about 8 pm, we circled in the air until 8:40 pm so I don't call that efficient for MSP. I think the captain should announce the delay and why. (as if we all don't know that we are just circling around the area, slowing down, speeding up, slowing down.) Thank you. Marilyn Fischer

Staff were friendly and happy. Delta could make sure passengers that don't have the app know of changes. Without Kayak I would not have known about the change of gate or the delay. Kayak was faster to notify me.

The flight used a B767 with a very old interior from before 2014. The entertainment system did not work at all during the flight despite attempts to reset the system. It was like they flew this route just to be competitive.

Delayed flight (1hour) plus a long layover after an overnight flight with no backup plane available.

The boarding process needs to be refined. Sometimes the gate crew calls out the zones and then flip to showing the.zones boarding on the gate monitor display. So, unless you are huddled around the gate lanes watching the monitor, you could miss your boarding zone. Suggest the zones be announced each time a new zone is allowed to board.

Flight delayed for two and half hours and then canceled altogether due to mechanical issues. No mechanic onsite to fix so had to send one from LAX.

This route with Delta always has delays or is cancelled. Aircrafts seem smaller and older. I fly Delta quite a bit - haven’t had issues with the international flights. But this route has always been the troublesome one

I’m so sorry, I can’t remember her name, I believe it was Dimpti. She was stellar, also a mature Asian flight attendant, lots of flowers in her hair, just as amazing! But literally the crew was AWESOME . Only downside is there weren’t any charging outlets. Maybe I needed to ask a flight attendant , but it would’ve been nice to have one easily accessible.

I boarded flight UA#1318 at Sacramento International Airport going back to Houston TX. The flight was scheduled at 5:10am. I was able to check in virtually using the United Airlines app. When I entered the airport, there was no one outside assisting with checked bags as it was for Delta Airlines. Immediately upon entering, there was a LONG, EXTREMELY LONG line to the kiosks to get boarding passes. I stand in line to get boarding passes then had to move to ANOTHER EXTREMELY LONG line to get my bags checked in. While standing in this line, we noticed an agent taking customers to 3 at a time to her station to check their bags in. Lucky for me, she called me back, checked my bags for me and I was on my way. I then encountered another long line at the TSA check and to avoid I ending up having to sign up for CLEAR to bypass it. So glad, I did.,...Both of my flights were great with no issues, butthe check in progress at Bush Airport was so much smoother. Check-in at SMF airport needs to be anaylzed and corrected. Do better United, I know you can....thanks

Pushed back only to get deplaned due to a tire damaged by ground crew. They did at least go pretty fast. The bathrooms should be banned under the Geneva convention. No room to even sit straight on the toilet. The under-seat entertainment units block what little leg room there is.

Essy to get on. The hostess gave very little pop, the plane was late getting in, and we are still waiting for our bags. This sucks. :/

United airlines has the best customer experience from booking to arrival. I always fly United airlines. The mileage program is excellent

Older aircraft, no meal, only food was for purchase. Not impressed United.

Not pleasant trip cross country when the entertainment and WiFi system not working. No entertainment for entirety of route. Staff was rather nonchalant in that they dismissed the problem due to age of plane. It would have been nice to know this up front so I could have come prepared to read or download movies before boarding Coincidentally or not, there was a similar issue with the entertainment system on my previous flight I took on my fist leg of the trip. There are no seat TVs, so you must rely on the app when it works. United can do better. Also, what use it it to pay for boarding group 2 when half of the passengers are in the same line as you?

Premium Plus is a really good idea for longer flights

Lately I like the planes have been exceptionally filthy. There’s lines of dust and dirt all across the ceiling in the vents, and the cracks in between the seats are literally full of food. It’s definitely not the quality of service that I was used to with United. I’m also very disappointed with the Wi-Fi! All I wanna do is knock out a few work jobs while I’m trapped in my seat And it spools so bad. They did provide me with a refund, but the process of getting that refund is so complicated. It’s unfortunate.

Excellent flight. Smooth, efficient boarding. Quick flight. Arrived early at STL.

The flight was on time and arrived early. The crew were friendly and helpful.

Overall experience was great. Flights were almost on time in departing and we arrived at our destination as scheduled. No issues with amenities or flight crew. Everything went well as as expected. Will fly again with American Airlines in the future!

Horrible. Both legs of my flight were delayed more than 6 hours. No compensation, no screens on the plane, and the plane was not clean.

The flight was smooth, the pilot kept us informed about delays and we arrived more of less on time

The flight was flawless and we even arrived between 20 and 25 minutes early!

Always seated jammed in rear of aircraft Admirals Club food at DFW terminal D was absolute worst food experience and I pay $600/year to eat this dried out junk

Mostly good. Flight was crowded but Airline personnel were very friendly & accommodating. It would be good to have savory snacks rather than just sweet Biscoff cookies.

It was a red eye flight, so no meals were provided, but it was fine with snacks. The seats felt cramped and almost too narrow.

Very crowded flight but what can you expect these days?? Crew was accommodating.

The seats in economy were appeared to be quite thin and lack sufficient cushioning to be comfortable. Perhaps it was my seating position but the plane seemed notably load.

It was ok. It was expensive to check 2 bags ($75.00 per bag), and then it took a long time to wait for shuttle to take us from one terminal to the terminal where the plane was taking off at LAX. And all of this for a flight where we had to pay for any food or drink that was not water.

It didn’t happen. I booked it and then was told it wasn’t available and then forced to pay far higher prices for a worse option

A 630departure flight Delayed 6hours! They changed my gate, I moved to the new gate. Had our flight on the screen for 12noon departure. I go get above to eat, check screen again and the flight was gone, no notice no announcement, nothing!! They sent my bag on the flight I wasn’t on, got it back to me 3days later. Thank goodness they did refund my money but I will NEVER fly them again.

Due to weather, my flight was delayed, further delayed, then canceled. I eventually got through to a support person who helped me find a different route out of MSP, but to get to DIA, they didn't want to, but eventually did help with the connection ticket purchase. But even this replacement flight was delayed time and time again, and I would have missed my connecting flights and I didn't want to get stuck in a layover city, so after 12 hours at the airport with two young boys who were very tired, we just cancelled our plans and spent the week at home, instead of Nana's.

Plane and crew on board were fine. Everything else was terrible.

When I wanted to check in 3 hours prior to boarding time, the employees mentioned “a little over an hour delay” so I waited for an hour then I went to go look for food in the terminal and most people from that flight were in the same area looking for food. Finally I decided after food to check to see if it’s anytime closer and now it’s 2 mins until boarding closes?! What are you kidding me? I didn’t receive anything via sms about boarding now nor via email or on the intercom. I luckily made it through, barely, and then there’s no room for my carry on mind you I’m in the very first row so I had to place my purse in one further row back and my carry on sections down. Not sure who pays for better seats to get your stuff placed all over the plane but that was the worst experience I’ve ever had flying with anyone.

This airline sucks. They offer low rates then charge you for everything, the app does not work well, the seats are the most uncomfortable. Maintenance issues on the flight, and you still have to sit through their credit card commercials. People are nice enough but does not make up for overall poor experience.

Cancelled flight after I arrived at airport after 75 min drive and parking. Next flight was 4 days in the future. Had to scramble and buy a much more expensive flight on another carrier.

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.

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

Information on your arrival and departure airports