STL - ONT

$94 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 3/18. 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, 0 bags

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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Everything you should know

Cheapest round-trip
$190
Overall average: $348
Frontier
Wed 4/8Thu 4/16
STL - ONT • 1 stop
Cheapest one-way
$94
Typical prices: $128-$230
Frontier
Wed 3/18
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
Las Vegas (LAS)
Cheapest • Avg $320 (round-trip)
Phoenix (PHX)
Shortest trip • 5h 55m (one-way)
Insights
Insights
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Insights
When to book
3 weeks
in advance
Our data shows that travelers who book at least 3 weeks in advance save around 31% compared to booking last minute.
Insights
Insights
Insights
Insights
When to travel
November
Cheapest • 15% price drop
July
Most popular
Good to know
Good to know
+1
+1
Good to know
Good to know
+1
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!
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

Wed, Apr 8 - Thu, Apr 16
Frontier Logo
8:16 pm - 11:56 pm
STL
-
ONT
5h 40m
1 stop
Frontier Logo
11:44 am - 9:00 pm
ONT
-
STL
7h 16m
1 stop
$190Frontier
Wed, Mar 25 - Thu, Apr 9
Frontier Logo
12:14 pm - 9:03 pm
STL
-
ONT
10h 49m
1 stop
Frontier Logo
6:20 am - 9:48 am
ONT
-
STL
25h 28m
1 stop
$192Frontier
Wed, Mar 25 - Tue, Mar 31
Frontier Logo
8:12 pm - 11:59 pm
STL
-
ONT
5h 47m
1 stop
Frontier Logo
6:15 am - 9:48 am
ONT
-
STL
25h 33m
1 stop
$196Frontier
Wed, Mar 18 - Tue, Mar 31
Frontier Logo
8:12 pm - 11:59 pm
STL
-
ONT
5h 47m
1 stop
Frontier Logo
6:15 am - 9:48 am
ONT
-
STL
25h 33m
1 stop
$197Frontier
Tue, Mar 17 - Tue, Mar 24
Frontier Logo
8:06 pm - 9:03 pm
STL
-
ONT
26h 57m
1 stop
Frontier Logo
6:15 am - 9:49 am
ONT
-
STL
25h 34m
1 stop
$201Frontier
Mon, Mar 16 - Mon, Mar 23
Frontier Logo
8:12 pm - 11:59 pm
STL
-
ONT
29h 47m
1 stop
Frontier Logo
3:30 pm - 11:19 am
ONT
-
STL
17h 49m
1 stop
$203Frontier
Wed, Apr 8 - Thu, Apr 16
Frontier Logo
8:16 pm - 11:56 pm
STL
-
ONT
5h 40m
1 stop
Frontier Logo
11:44 am - 9:00 pm
ONT
-
STL
7h 16m
1 stop
$211Frontier
Wed, Mar 18 - Mon, Mar 30
Frontier Logo
8:12 pm - 11:59 pm
STL
-
ONT
5h 47m
1 stop
Frontier Logo
9:49 pm - 11:19 am
ONT
-
STL
11h 30m
1 stop
$214Frontier
Wed, Mar 11 - Mon, Mar 16
Frontier Logo
8:12 pm - 11:59 pm
STL
-
ONT
5h 47m
1 stop
Frontier Logo
3:30 pm - 12:15 pm
ONT
-
STL
18h 45m
1 stop
$216Frontier
Thu, May 14 - Fri, May 15
Frontier Logo
8:12 pm - 11:55 pm
STL
-
ONT
5h 43m
1 stop
Frontier Logo
6:15 am - 2:12 pm
ONT
-
STL
5h 57m
1 stop
$217Frontier
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 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 March and July, where the average cost of round-trip tickets is $449 and $381 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 3 weeks before departure, which saves you about 31% compared to booking last minute. For the absolute cheapest price, our data suggests you should book 11 weeks before departure.

Good to know

Low seasonSeptember
Cheapest flight$94
Best time to beat the crowds but there is an average 2% increase in price.
Most popular time to fly with an average 10% 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 $94 for a one-way ticket and $190 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?

    SkyTeam, Star Alliance, and oneworld are the airline alliances operating flights between St. Louis and Ontario, with SkyTeam 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 $388 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 4295 reviews
8.0Comfort
8.6Crew
7.5Entertainment
8.1Boarding
7.0Food
Airline reviews

The charges were ridiculous for an hour flight and the turbulence was very scary.

2.0 MediocreDarcey, Feb 2026
SAN - SJC
Read more Southwest reviews

The charges were ridiculous for an hour flight and the turbulence was very scary.

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

3 hour delay. Had to change plans and was still delayed.

The flight crew was extremely rude and especially not helpful when our flight was delayed.

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.

Still a fan of open seating. Flight was on schedule and arrived on time. The 737 MAX is very comfortable.

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

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.

Delays delays delays. Late taking off, late landing, wait for a gate, etc.

Delta continues to set the benchmark for traveler-friendly service with minimal disruption and clear communication within the mainland US (coast to coast). I am consistently pleased to be a Delta customer, and this experience once again met my expectations. There was a brief delay departing from MIA due to a technical issue that required the aircraft to return to the gate. However, the situation was handled professionally and transparently. Fortunately, my planned layover allowed ample buffer time, so the adjustment caused no stress. Overall, another smooth and reassuring experience.

Awesome! On time flight, early arrival, and a complimentary upgrade!

Was forced to check in my small carry on, even though I informed the crew it has very fragile items inside

They double booked seats, the gate staff changed my ticket as I was boarding she went over to the computer and changed it without telling me. She messed up an entire three row section for me and others. Other travelers were outraged but the gate staff were so rude, so condescending saying it wasn't their problem to solve. I would rate this a zero if I could. Will not fly Delta again I'll stick with United and American.

I usually get upgraded so my experience is usually amazing. I did not get upgraded this time - which was fine - but the wifi had issues, the monitors were going in & out, & (though not Delta's fault) one of the gentlemen next to me desperately needed a shower.

I really liked the legroom. I am 6’4”.a at For some reason our seats were not together and using the app to fix it didn’t work. Passengers were nice enough to move for us but you should absolutely ensure a parent sits with their child.

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.

They changed planes and the new plane couldn’t carry enough fuel to fly across the country so we had to stop in Kansas City to refuel. Flight was delayed .

Flight was too crowded and seats are too small, especially since passengrs are getting larger. Having a middle seat is ALWAYS tough! Woman on my left was large & kept creeping in to my space. Flight personnel were great! Have more savory rather than sweet snacks please.

The crew took good care of us. The flight from ATL to SFO is a longer one, and there were multiple beverage offerings. I like the 757's that Delta uses. Good airplane that is comfortable. I do wish Delta would separate Priority boarding from the better seats. I would gladly take a smaller seat in an open row than be jammed into Comfort just to get priority boarding, just to make sure I don't have to check a bag.

it was a very short flight so my expectations were low.

Very disappointing given gate agent behavior. Filed a formal complaint with United.

Flight delayed. WiFi connectivity very poor if not existant. Last minute arrival forced me to run to catch my connection.

The power at the seat didn't work and the seat itself was difficult to adjust - this was a business class seat. Flight attendant gave me miles to compensate. The attendant was very professional and on top of his game the entire flight.

the whole trip was smooth, and as comfortable as flying is these days. flight crew was friendly and very courteous and helpful.

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.

First class ticket gets you a choice of chips or nuts. . Just like economy Southwest. Also no screen in the seats. This is first class???!

Flight arrived 30 min early and bag was waiting at the baggage pickup. United Club HNL was one of the nicest in the system

Yet another flight in which beverage and snack service was skipped. Other that that, firmly mediocre. Landed early, to gate late due to congestion at the gates. Airline's fault or airports fault: unknown.

Teeny tiny bathrooms, crew was not realistic about when we'd arrive.

The flight was significantly delayed for 6.5 hours because of snow. There was no communication once the plane returned to the gate regarding when the flight would resume. Other flights were departing while our flight was being unloaded for reasons unknown. Our flight also seemed out of the queue regarding further deicing, refueling, and waiting to Taxi to the runway.

They are always late and seats was also not having working charger

did not have enough meal for first class passengers so offer us snack

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 about the flight was lovely. My only suggestion would be to offer a few more options of tv series from Apple TV or HBO.

After the door had been closed, the cockpit makes an announcement that catering is running late and it is not the airline's fault. It is their fault in the sense that we had to sit for 2 hours or more when we could have stayed in the terminal. Poor communications between catering and airline. This caused a young man to lose his temper and he went storming out hitting objects. He had complained to the gate agent that he had already waited at the gate 7 hours and when can the airplane leave? Airilnes do a poor job of explaining delays, maintenance issues, etc. whereas being truthful may gain more sympathy or understanding.

We were told the flight was delayed 5 times, then it was moved to the next day.

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

Frontier.. nickel and dime add-ons. Flight late, on time, late again, last minute gate change, arrival gate required a shuttle to the terminal. They sure keep you guessing.. if you like a little chaos and airport anxiety, this is the airline for you!

This is my second time flying with Frontier. My current experience was very favorable. The staff from the gate to the plane was friendly, warm and professional. The food options lacked in my opinion. This area needs some attention in my opinion.

There was no food and no entertainment, so I'm not sure why these are even in the survey, as my understanding is frontier does not ever offer food without a few, not even a snack, and there are no screens so unless the flight safety talk is our entertainment why ask how we liked it?. One of the flight attendants say in the back of the plane as people filed in to their seats, yelling orders about where to put baggage and telling people to hurry up. It was the least professional experience I've ever had on a flight.

Very well recently! Frontier is improving and less harrassing customer on luggages! Positive!

Good for a budget airline! It was easy to get on, staff was really nice. Can’t say anything about the food or entertainment because it wasn’t available, which is fine.

I am writing to express my disappointment with my recent Frontier Airlines flight. I was charged $99 at the gate because my bag was said to be too large, yet once onboard there was no available overhead bin space, and I was required to place the bag under the seat in front of me anyway. This made the charge feel unnecessary and unfair. Additionally, before the flight even took off, I was asked to move from the seat I paid for into a middle seat so another passenger and her cat could have my seat to themselves. I was not offered compensation or an explanation for being moved from a paid seat. Between the unexpected bag fee and being forced to give up my seat, this experience fell well below acceptable customer service standards. I would appreciate a review of this situation and appropriate compensation.

It was costly and difficult to check in. $85 to take a small suitcase with me, carry on or checked and $75 on the return trip, Plus $25 if I didn't check my self in check in $25, because I couldn't do it on the kiosk. Small very uncomfortable seats, waited on the runway for near an hour each way. It was my worst flight to date.

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

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

Information on your arrival and departure airports