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Cheap Flights from Ontario International to St Louis

Compare Ontario International to St Louis flight deals

Find the cheapest month or even day of the year to fly to St Louis

Book the best St Louis fare with no extra fees

Flight deals from Ontario International to St Louis

Looking for a cheap last-minute deal or the best return flight from Ontario International Airport to St Louis Airport? If you want to travel next month, return fares start from R 3,787. Find the lowest prices on one-way and return tickets right here.
St Louis.R 1,344 per passenger.Departing Tue, 11 Aug.One-way flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from Ontario International on Tue, 11 Aug, arriving in St Louis.Price includes taxes and charges.From R 1,344, select.
St Louis.R 2,141 per passenger.Departing Wed, 2 Sep.One-way flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from Ontario International on Wed, 2 Sep, arriving in St Louis.Price includes taxes and charges.From R 2,141, select.
St Louis.R 2,142 per passenger.Departing Sat, 17 Oct.One-way flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from Ontario International on Sat, 17 Oct, arriving in St Louis.Price includes taxes and charges.From R 2,142, select.
St Louis.R 2,507 per passenger.Departing Thu, 10 Dec.One-way flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from Ontario International on Thu, 10 Dec, arriving in St Louis.Price includes taxes and charges.From R 2,507, select.
St Louis.R 3,226 per passenger.Departing Fri, 17 Jul.One-way flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from Ontario International on Fri, 17 Jul, arriving in St Louis.Price includes taxes and charges.From R 3,226, select.
St Louis.R 3,288 per passenger.Departing Tue, 24 Nov.One-way flight with Delta.Outbound indirect flight with Delta, departs from Ontario International on Tue, 24 Nov, arriving in St Louis.Price includes taxes and charges.From R 3,288, select.
St Louis.R 3,891 per passenger.Departing Sun, 17 Jan.One-way flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from Ontario International on Sun, 17 Jan, arriving in St Louis.Price includes taxes and charges.From R 3,891, select.

Find the cheapest month to fly from Ontario International to St Louis

We’re always keeping an eye on fares, so you can find the best one in seconds. It looks like Ontario International to St Louis flights are currently cheapest in August.
Jul
from R 3,226
Aug
from R 1,344
Sep
from R 2,141
Oct
from R 2,142
Nov
from R 3,288
Dec
from R 2,507
Jan
from R 3,891
Feb
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Mar
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Apr
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May
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Jun
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Ontario International to St Louis: Alternative routes

Compare routes from Ontario International to St Louis below. You may find an airport to fly into that's cheaper, faster, or easier than St Louis.

St Louis

20km from central St Louis
ClosestCheapest
from R 1,344
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Belleville

32km from central St Louis
from R 2,758
Search flights

Ontario to St Louis: Flight information

The things to know before you go.
Cheapest flight foundR 1,344
Cheapest month to flyAugust

Finding cheap flights from Ontario International to St Louis: Frequently asked questions

The best price we found for a return flight from Ontario International to St Louis is R 3,787. This is an estimate based on information collected from different airlines and travel providers over the last 4 days and is subject to change and availability.
Currently, there are no airlines that fly direct from Ontario International to St Louis. But we found flights with one or more stops from R 3,787.
As of July 2026, there are no flights flying from Ontario International to St Louis.
The cheapest month to fly from Ontario International to St Louis is usually August.
After crunching the numbers on our flight calendar, we found that it's currently cheapest to fly from Ontario International Airport to St Louis Airport on Tuesday, 11 August 2026.
No airlines currently offer direct flights between Ontario International Airport and St Louis Airport. Most routes have one or more stops.
We show every price from over 1,200 airlines and travel agents, comparing them all so you don’t have to. If you know you want to fly to St Louis but you’re not ready to book, set up a Price Alert. We’ll track prices for you, and let you know when they rise or fall.

We crunched all the numbers in our flight calendar and it looks like the cheapest time to book a flight to St Louis is around 40 days in advance, so don’t leave your flight to the last minute.

Currently, Frontier Airlines offers the cheapest flight tickets to St Louis.

Travelling from Ontario International Airport (ONT) to St Louis Airport (STL): what you need to know

  • St Louis's timezone is UTC-6, which makes St Louis two hours ahead of Ontario.

  • For a stress-free journey, turn up at the airport two hours ahead of international flights and an hour before domestic departures. This ensures you have enough time to board your ONT to STL flight.

  • Be prepared for longer queues in popular months such as July. Arriving up to four hours ahead of an international flight and two hours for domestic departures is a wise move.

  • Consider adding a stopover when booking your ticket from Ontario International Airport to St Louis Airport. Simply deselect 'Direct flights only' to break up your trip, or enjoy a detour to a new and interesting place. Here's where you can stop between ONT and STL:

    • Denver International Airport

    • Phoenix Sky Harbour Airport

    • Harry Reid International Airport

Handy information about Ontario International Airport (ONT)

  • You'll find ONT at 2900 E. Airport Drive.

  • Ontario International Airport has an excellent on-time record, making delays less likely. Departures from ONT land on schedule 83% of the time.

  • Central Ontario to Ontario International Airport is around 10 kilometres. Depending on traffic, it'll take about 15 minutes to get there if you're catching a taxi, ride-sharing or driving.

  • Planning to take public transport? Expect a trip time of around 45 minutes.

  • Catching an early flight from Ontario International Airport to St Louis Airport? Avoid the stress of rushing to the airport (and sneak in some extra snooze time) by choosing one of these hotels near ONT:

Arriving at St Louis Airport (STL)

When to fly to St Louis Airport (STL)

  • It's time to plan your dates for your flight from Ontario International Airport to St Louis Airport. July is the most popular month to visit St Louis. If you prefer a more laid-back vibe, go in March.

  • Lock in your flight from Ontario International Airport to St Louis Airport for July if you want to go to St Louis during its warmest month. You can expect temperatures of between 17ºC (63ºF) and 33ºC (91ºF).

  • January sees average temperatures of between -7ºC (19ºF) and 8ºC (46ºF). Look for cheap tickets from ONT to STL sometime around then if you like cooler conditions.

Explore more of the United States

  • You've done St Louis, now it's time to explore other parts of the United States. Journey about 418 kilometres north-east to Chicago to check off its leading attractions. From Millennium Park to Art Institute of Chicago and Willis Tower, there's plenty to keep you busy.

  • Indianapolis is another well-known destination in the United States and is around 370 kilometres east of St Louis. No journey is complete without experiencing Lucas Oil Stadium, Eiteljorg Museum and The Children's Museum of Indianapolis.

Plan the rest of your trip from Ontario to St Louis

Prices shown on this page are estimated lowest prices only. Found in the last 12 days.