STL - ONT

$71 Find Cheap Flights from St. Louis to Ontario

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 9/14. 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 Ontario

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

Sun, Nov 2 - Mon, Nov 17
Frontier Logo
7:45 pm - 11:50 pmSTL-ONT
6h 05m1 stop
Frontier Logo
6:00 am - 1:57 pmONT-STL
5h 57m1 stop
$142Frontier
Find Deal
Fri, Sep 12 - Mon, Sep 15
Frontier Logo
7:55 pm - 7:54 pmSTL-ONT
25h 59m1 stop
Frontier Logo
8:59 pm - 9:06 amONT-STL
10h 07m1 stop
$143Frontier
Find Deal
Mon, Sep 22 - Tue, Sep 30
Frontier Logo
7:55 pm - 7:54 pmSTL-ONT
25h 59m1 stop
Frontier Logo
8:59 pm - 9:06 amONT-STL
10h 07m1 stop
$144Frontier
Find Deal
Tue, Sep 16 - Tue, Sep 30
American Airlines Logo
7:16 am - 11:57 amSTL-ONT
6h 41m1 stop
American Airlines Logo
1:10 pm - 10:50 pmONT-STL
7h 40m2 stops
$298American Airlines
Find Deal
Tue, Sep 16 - Tue, Sep 30
American Airlines Logo
8:50 am - 4:05 pmSTL-ONT
9h 15m2 stops
American Airlines Logo
1:10 pm - 10:50 pmONT-STL
7h 40m2 stops
$303American Airlines
Find Deal
Wed, Jan 7 - Wed, Jan 14
Delta Logo
7:30 am - 12:34 pmSTL-ONT
7h 04m1 stop
Delta Logo
1:00 pm - 9:37 pmONT-STL
6h 37m1 stop
$317Delta
Find Deal
Tue, Dec 9 - Sat, Dec 13
Delta Logo
7:30 am - 12:31 pmSTL-ONT
7h 01m1 stop
Delta Logo
7:00 am - 6:02 pmONT-STL
9h 02m1 stop
$318Delta
Find Deal
Sat, Feb 7 - Wed, Feb 11
United Airlines Logo
11:20 am - 8:58 pmSTL-ONT
11h 38m2 stops
United Airlines Logo
5:05 am - 1:16 pmONT-STL
6h 11m1 stop
$332United Airlines
Find Deal
Thu, Nov 20 - Sun, Nov 23
Southwest Logo
10:15 am - 5:20 pmSTL-ONT
9h 05m1 stop
Southwest Logo
12:35 pm - 11:10 pmONT-STL
8h 35m1 stop
$387Southwest
Find Deal
Thu, Nov 20 - Sun, Nov 23
Southwest Logo
10:25 am - 3:20 pmSTL-ONT
6h 55m2 stops
Southwest Logo
2:15 pm - 11:30 pmONT-STL
7h 15m1 stop
$392Southwest
Find Deal
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.

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

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

If your flying dates are flexible, you should consider flying to Ontario on a Tuesday, as we generally find the cheapest rates on that day for this route. On the other hand, Sunday is the most expensive day to fly from St. Louis to Ontario. For your return ticket, we recommend flying on a Monday and avoiding Sundays for the best deals.

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 February, where tickets cost $256 (return) on average. On the other hand, the most expensive months are March and September, where the average cost of round-trip tickets is $576 and $486 respectively.

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

To calculate weekly average prices, KAYAK takes all prices for each week before departure 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 average of all the values for each week.

To get a below average price on the flight from St. Louis to Ontario, you should book around 2 weeks before departure, which saves you about 37% compared to booking last minute. For the absolute cheapest price, our data suggests you should book 11 weeks before departure.

Good to know

Low seasonMarch
Cheapest flight$71
Best time to beat the crowds but there is an average 54% increase in price.
Most popular time to fly with an average 2% 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 3 days, the lowest price for a flight from St. Louis to Ontario was $71 for a one-way ticket and $142 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?

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

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

    The two airlines most popular with KAYAK users for flights from St. Louis to Ontario are Southwest and Delta. With an average price for the route of $407 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 $362 and an overall rating of 7.9.

  • 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 5 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.
8.0
SouthwestOverall score based on 4242 reviews
8.1Boarding
7.5Entertainment
8.6Crew
8.0Comfort
7.0Food
Airline reviews

Very smooth checking in our luggage with a super pleasant SW agent. I enjoyed a fun entertaining movie.

10.0 ExcellentGordon, Jul 2025GEG - OAK
Read more Southwest reviews

Very smooth checking in our luggage with a super pleasant SW agent. I enjoyed a fun entertaining movie.

First time traveling on Southwest since bag fees were implemented. Usual good service. Just more expensive now.

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

Boarding process, crew were good. But the seats were so uncomfortable that was all I could focus on. I literally had to sit forward so that all 3 of us could fit in row. I will try to avoid Southwest in the future for any flights over 60 minutes.

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

Great experience flying Southwest. The crew was really kind and helpful, and very friendly with our toddler.

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

Plane late from DC to Austin 30 minutes. Crew made up much of the time enroute to San Diego.

Fine, but how to board on SW versus othrr airlines, is just lame. Goood staff though and all was solid otherwise.

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

Great flight with Delta! Boarding was quick and easy, the amenities were solid, and the plane was in great shape. The flight attendants had a fun, lively energy while staying professional. All in all, a smooth trip — even managed to catch up on some rest. Thanks, Delta!

I was uncomfortably cold on the plane. Other than that it was uneventful and therefore as enjoyable as a plane ride can be.

Food was surprisingly good but the WiFi was not great

My flight was extremely cold. I had a jacket and a cover was left in each seat. The cover was extremely thin and I have a disability, fibromyalgia and arthrithis and AC air is the worst. I closed my vent and my husbands vent and it still was frigid. I asked the attendant if I could get another cover and she quickly almost dismissively and totally unconcerned stating, (I quote) (one per chair) and walked off so quickly that I didn't get a chance to explain to her that I literally have adisability. I didnt want to make a seen so I set on that flight for over 5 hours in pain, joints locking up and extremely uncomfortable. When my fibromyalgia flares up my joints not only ache but they will lock up also and it takes me days to get back to my regular self even though I take medication for it. I felt like it would not have hurt anyone at all for her to just give me an extra cover because I'm sure they have all types of medical issues in people that fly every day.

My flight was canceled after being rescheduled for four days canceling my trip. Kayak and everyone affiliated with it I.e the airlines, and just fly have been excruciating to deal with. My trip to visit family had to be canceled as there was no way to make it. I am furious at all of you.

They delayed our flight because of bad weather in NY which was completely understandable. Then they cancelled our flight and a later flight that evening. The earliest we could fly was the next morning. We ended up buying last minute tickets on another airline and made it home slightly delayed but safely that evening. Delta kept saying it was weather related but if that was the case how did we make it back on another airline? The weather in NY was cloudy but not bad.

Not a "Delta" issue, but a JFK issue: We booked a connecting flight with 3 1/2 hours between to clearn immigration and customs. Our inbound flight (BCN to JFK) was on the taxiway 45 minutes which ate into our layover time. Immigtration was insanely quick with the CBP MPC app; however, clearing TSA (again, after we were ALREADY cleared in Spain on the inbound international flight) took over 95 minutes. This left us with 10 minutes before boarding the connecting flight (JFK to SAN) to walk to the far end of Terminal 4 and try to find food. We didn't find any food that could promise to serve us in under 10 minutes so we boarded the Delta flight after coming off a plance and an 8-hour flight knowing that we wouldn't be served any food on the next 5 1/2 hour flight. I feel like Delta needs to put pressure on the JFK TSA to open more screening stations (by our count, we saw only 5 scanners open and a line of - as we said - over 90 minutes. The insult is that we WERE ALREADY SCREENED through TSA, but as you come off one flight into the USA, you have to go through the whole process again. It seems like if you have a connecting flight, there should be a way to pass through immigration and customs without needing to return through TSA.

There are 4 flights in consecutive gates with about the same departure time. Two flights were boarding at the same time. One was delayed or boarding would be happening at the same time. I am not sure what Delta and LAX need to do to have a better layout at the end of Terminal 2

5 hours of delay that could've been much shorter if Delta had taken the 1 hour delay they imposed on the flight before boarding to run any of the plane checks required for flight to find the hydraulic issue that required nearly 3 hours to fix. $24 of meal credit buys a sandwich and a soft drink. Poor communication within the terminal about what gate we'd be re-boarding from and when we'd be re-boarding.

The entertainment and wifi mostly didn't work on this flight.

The flight was comfortable with the exit row and great service

Plane was crowded and even when we hit altitude, the plane was hot, not enough air flow.

1. when we went to check in, our 2 first class seats had been CANCELED and the flight was sold out. This was done without our prior knowledge. It was all we could do to restore one first class seat for my wife and I flew economy. 2, Our flight home was scheduled to leave at 10:30 pm. Due to tsunami warnings, the roads were closed and our flight status was uncertain as to whether it would leave as scheduled. It was announced that it would now leave at 11:20 pm and the roads were now open since the tsunami had come and gone. We made a mad dash to the airport and checked in. Delays were announced at 12:30 pm, 1:30 am, 2:30 am and at 3:30 am it was canceled. Since this was a flight due to natural (tsunami) causes, there was no compensation. We were told to return at 1:00 pm the next day and our baggage would be kept on the plane since the same plane was going to leave at 1:00 pm. We had to return to our hotel for the rest of the night. The same plane did not leave at 1:00 pm and our baggage was gone! All in all, it was a miserable performance by UA. Information was hard to obtain and no one knew what was going on and what was going to happen. Hundreds of passengers slept on the floor, chairs, etc. No food and no water was made available to the passengers. It was a situation where UA could care less what was going on. As a one million mile flyer, I had not experienced anything like this before and it was hugely disappointing!

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.

Boarded plane and then delayed 1.5 hours while on the plane

Horrific. They missed my connecting flight to San Diego. I didn’t get there until Monday at 9am when I had a mandatory court settlement conference scheduled at 6am since we had parties on the east coast. This caused many issues. All because United apparently forgot to hold the doors open until my flight landed that only had a 10 minute delay. This was the last flight to Southern California. So I couldn’t even rent a car to finish the trip. United cannot be trusted when traveling on specific days and times since weather didn’t have anything to do with the delays.

My flight was delayed a very short period of time but they did not hold my connecting flight to San Diego, also through United. So they closed the doors before we got off our plane. They would only have to help the door open for another five to ten minutes. So I missed a court deadline for a manditory mediation settlement conference for my client. I had to get an associate to be there in person and be on the phone with him relaying what he needs to do the entire time. The court was very upset with me and so was my client. United cannot be trusted.

We were given vouchers we couldn’t use with a 5.5 hour delay

Really good 😊 the woman at the gate entrance was a little rude checking in our carry-on but i dont think she worked for the airline, she worked for the airport at sacramento, other than that amazing.

Boarding was mayhem. Late boarding by 15 minutes because of lack of staff (missing 1 flight attendant. We had to wait for an arrival of another plane before we could board). Flight was a little rough, but cannot blame on airlines.

Delayed flight that lead to a missed connection and a 5-hour trip became a 12-hour flight 🙄

There is no room, no gluten free options, or any free internet/entertainment. You have to bring your own tablet or smartphone because there are no screens.

Amazing food, great staff, with one noticable detail missing ...but no seat entertainment in any of aircraft ...I am not a fan

Boarding gate in Honolulu was staffed with a great clerk with a soothing voice despite the flight delay of over an hour. Flight attendants in the plane were all grumpy, not pleasant looking bunch. Their sour attitude showed throughout the flight. Inly able to get a select few movies started. Most of the movie links in the “free entertainment” did not work.

This was a horrible experience. For a first class experience, my chair was held together by 3M tape - and I have a photo. The crew weren’t very attentive, somewhat dismissive and forgot my drink and snack, the chair reclined about 3 inches on a 6-hour cross country flight. I was also not informed that there was no lounge available in Newark airport because of renovations, so all around this was one of the worst experiences and I would actively avoid both American and Alaska Air going forward.

Boarding was very efficient. Everyone got on board and we got on our way very quickly. It was frustrating that the entertainment app was not functioning properly. I was not able to activate some of the movies offered. The crew on this flight appears to be pretty grumpy. They had no smile on their faces. I felt like they were doing us a favor for being there.

Loved the staff, boarding and drink options! Wish the comfort of the seat could have been better nevertheless

Honestly, I haven’t flown American in years, probably due to the pandemic and my being unable to travel for certain periods in the last two years, but it was a good experience to dig out or obtain a new American Airlines account after many years of traveling for business with American in the past.

Long 5 hour and 45 min flight and only one drink service and cookie snack

One bottle of water and a package of cookies for comfort plus. We had to literally beg a flight attendant for an extra bottle of water later in the flight due to feeling dehydrated.

Great for the price. No wifi or entertainment, but gate agents and crew were fantastic and we boarded quickly and left on time.

sluggish boarding and arrival procedures, fake nice flight attendants, and lots of delays.

Disaster. They lied every step of the way. We ended up being delayed due to crew and then allegedly abandoned the flight because of a curfew at LGA. No rebooking to LGA at any reasonable time. No hotel. No meal vouchers. Had to sleep in the airport and fly to Newark instead. Will never fly Frontier again.

What I expected, nickeled and dined and a frontier flight attendant loudly complained about her job and lack of communication as she headed to the gate on her cell phone. Not professional.

As every law enforcement agency I could imagine surrounded the plane and we didn’t disembark for 2 hours and then had to stick around for another hour to go get our personal belongings after leaving them behind and being bused away from the plane, it was scary and inconvenient. We were given no information as to why this was happening. Lack of communication with passengers was disappointing.

After boarding and un-boarding twice over 6+hours, the flight was canceled.

Severe turbulence. Captain never came on to reassure passengers after things settled down.

My first flight was delayed 5 hours. The 2nd flight was canceled til the next day and the never even tried to compensate for it. Worse I was delayed again on the flight the rebooked me on.

Boarding in Orlando was not good. Giant mob at the gate, should have been lines.

Decent clean onboard experience. Okay discount airline experience. Unfortunately, any customer service interactions are difficult and unhelpful. There is no service. Also, a premium seat only gets you premium boarding if you line up first. Once they start general boarding you must go to the back of the line. Not very premium

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

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