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 9/18. 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

Sat, Nov 1 - Thu, Nov 6
Frontier Logo
4:51 pm - 8:42 pmSTL-ONT
5h 51m1 stop
Frontier Logo
6:00 am - 1:57 pmONT-STL
5h 57m1 stop
$142Frontier
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Fri, Sep 26 - Sun, Sep 28
Frontier Logo
9:35 pm - 12:43 pmSTL-ONT
17h 08m1 stop
Frontier Logo
8:59 pm - 9:06 amONT-STL
10h 07m1 stop
$143Frontier
Find Deal
Fri, Sep 26 - Sun, Sep 28
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, Oct 7 - Tue, Oct 14
Southwest Logo
5:10 pm - 10:05 pmSTL-ONT
6h 55m1 stop
Southwest Logo
4:25 pm - 12:30 amONT-STL
6h 05m1 stop
$188Southwest
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Thu, Nov 6 - Mon, Nov 10
 Logo
6:22 pm - 7:17 amSTL-ONT
14h 55m2 stops
 Logo
6:53 am - 9:07 amONT-STL
24h 14m1 stop
Thu, Oct 16 - Mon, Oct 20
 Logo
3:57 pm - 12:03 amSTL-ONT
10h 06m1 stop
 Logo
6:53 am - 9:07 amONT-STL
24h 14m1 stop
Tue, Oct 7 - Tue, Oct 14
Southwest Logo
2:55 pm - 8:40 pmSTL-ONT
7h 45m2 stops
Southwest Logo
2:30 pm - 12:10 amONT-STL
7h 40m2 stops
$226Southwest
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Sat, Feb 28 - Wed, Mar 4
Alaska Airlines Logo
2:55 pm - 10:37 pmSTL-ONT
9h 42m1 stop
Alaska Airlines Logo
11:30 am - 11:56 pmONT-STL
10h 26m1 stop
$242Alaska Airlines
Find Deal
Tue, Dec 9 - Sat, Dec 13
American Airlines Logo
2:37 pm - 6:19 pmSTL-ONT
5h 42m1 stop
American Airlines Logo
3:04 pm - 10:47 pmONT-STL
5h 43m1 stop
$243American Airlines
Find Deal
Tue, Dec 9 - Sat, Dec 13
American Airlines Logo
11:35 am - 6:19 pmSTL-ONT
8h 44m2 stops
American Airlines Logo
6:00 am - 3:27 pmONT-STL
7h 27m1 stop
$248American Airlines
Find Deal

Everything you should know

Top airlines
Frontier
Cheapest • from $142 (round-trip)
Southwest
Best reviews • 8.0 score
Airline reviews
Airline reviews
+1
+1
Airline reviews
Airline reviews
+1
When to book
2 weeks
in advance
Our data shows that travelers who book at least 2 weeks in advance save around 37% compared to booking last minute.
Insights
Insights
Insights
Insights
When to travel
February
Cheapest • 31% price drop
December
Most popular
Good to know
Good to know
+1
+1
Good to know
Good to know
+1
Cheapest round-trip
$142
Overall average: $350
Frontier
Sat 11/1Thu 11/6
STL - ONT • 1 stop
Cheapest one-way
$71
Typical prices: $223-350
Frontier
Thu 9/18
STL - ONT • 1 stop
Start a new search
KAYAK searches 100s of sites at once to find you the best travel deals.
We hope you love your trip to Ontario!
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 $417 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 4248 reviews
8.0Comfort
8.1Boarding
7.5Entertainment
7.0Food
8.6Crew
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.

Great. Quick and quiet and east. The breakfast choices were a welcome surprise!

The stewardess hit me with the food kart twice on the head and didn't say I'm sorry once. The same stewardess gave me a warm Apple Juice with No ice. The Flight was delayed for Departure 6 times, starting from 2:36pm, finally taking off 7:50pm. I was late picking up my child from the sitter by 3 hours.

Did not get the seat I selected and paid for.

My flight was delayed for several hours. Sitting at gate 16 for several hours, I got a text from Kayak the gate changed to 9 before it was announced. Very bad communication at each gate from American Airlines employees. I received 10 notifications of delay from Kayak. My vacation started off horrible! I will write to American Airlines corporate office also.

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.

Seats were new and comfortable. Staff was fine. Missed my connection due to weather -which wasn’t their fault- but got no help at all. Gate staff sent me to customer service, which was and stayed unstaffed. Sign with QR code directed me to call or chat. Chat was useless. Call was returned after an hour. No itinerary offered by Frontier could get me home in less than 30 hours. Rebooked with another airline and got a partial refund that came to about 10 percent of what I paid to get home.

Finally a Frontier on time and efficient. I've had problems before with your airline, but this time everything went fine.

The experience was good. No frills but I got there safe and sound and on time.

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.

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

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