Cheap flights from Ontario to St. Louis from $107
This is the cheapest one-way flight price found by a momondo user in the last 72 hours by searching for a flight from Ontario to St. Louis departing on 9/2. Fares may change, and may not be available for all flights or travel dates. Click the price to refresh the search for this deal.
Discover deals from 900+ travel sites with momondo.
Save money when you book flights with momondo
Big names and deals
Big names and deals
Search 100s of travel sites to compare prices.Filter for what you want
Filter for what you want
Free Wi-Fi? Stopover? Instantly customize your results.Trusted and free
Trusted and free
We’re completely free to use - no hidden charges or fees.Price Alerts
Price Alerts
Not ready to book? to track prices.Find the cheapest flights from Ontario to St. Louis
Cheap round-trip flights
Cheap one-way flights
Cheap last minute flights
Frontier flights from Ontario to St. Louis
Our best Frontier deals on Ontario to St. Louis flight tickets
Southwest flights from Ontario to St. Louis
Our best Southwest deals on Ontario to St. Louis flight tickets
See travel insights to St. Louis from
How to get the cheapest flight ticket from Ontario to St. Louis
Look no further. We've gone through all the searches for this route on momondo so you have the important information and insights to find the cheapest flight ticket for your trip
What is the cheapest month to fly to St. Louis?
In general, August is the cheapest month to fly from Ontario to St. Louis. Due to it being the ‘off-season’ during this time, you can expect flight prices to be around $214. The month of September is another great option to travel to St. Louis, with average flight prices from Ontario averaging around $267.
What is the cheapest day to depart on your flight to St. Louis?
The cheapest day to depart on your flight to St. Louis is on a Tuesday when prices can be found for as low as $385. This is often the case because there is less demand to fly during this day of the week. If your travel schedule is flexible, try to avoid departing on a Monday because tickets tend to average around $437. These prices are subject to change though, so be sure to set up a Price Alert for flights to St. Louis.
What is the cheapest time of day to depart on your flight to St. Louis?
Flying to St. Louis from Ontario in the morning is the least expensive time of day to depart. momondo users have found prices as low as $417 when looking at flights departing in the morning. In the evening is when there is more demand to fly to St. Louis, so prices are often more expensive at around $425 per ticket.
How far in advance should I book a flight to St. Louis?
You are more likely to see cheaper flights to St. Louis from Ontario when booking 5 weeks ahead of your departure date. In general, you can expect to find flights to St. Louis for around $345 when searching 5 weeks out.However, flight prices might be lower outside of this timeframe. For example, people recently found flights to St. Louis from Ontario for as low as $233 on momondo.
What is the cheapest airline that flies from Ontario to Lambert-St Louis?
Frontier, Delta, and Hawaiian Airlines are the most popular carriers operating from Ontario to Lambert-St Louis
What airlines fly to St. Louis?
American Airlines, Southwest and Frontier are the top three most popular airlines that fly to St. Louis from Ontario according to our data. American Airlines is the first choice among our users, with 39% of people opting to fly with this airline when traveling to St. Louis. Keep in mind that there are 7 different airlines that fly to St. Louis on a routine basis, so you have a few additional options to choose from.
When to book flights from Ontario to St. Louis
Cheap Ontario to St. Louis (ONT to STL) flight deals and tips
Find info about flight duration, direct flights, and airports for your flight from Ontario to St. Louis
How far is Ontario to Lambert-St Louis by plane?
There are 1552.8 mi between Ontario and Lambert-St Louis. 5h 29m is a normal flight duration for this route.
When did momondo last update prices for flights from Ontario Airport to Lambert-St Louis Airport?
Prices for flights from Ontario Airport to Lambert-St Louis Airport are updated daily.
How many operators does momondo search for flights from Ontario Airport to Lambert-St Louis Airport?
There are 5 operators available for flights from Ontario Airport to Lambert-St Louis Airport as of June 2025.
How old do you have to be to fly from Ontario Airport to Lambert-St Louis Airport?
The minimum age for a child to fly alone is five, but airlines that offer an unaccompanied minor (UNMR) service may have their own age limitations. Flight duration, scheduling, and layovers are among the considerations that may influence age limits. We recommend that you double-check with the airline you are booking with for travel from Ontario Airport to Lambert-St Louis Airport.
What documentation or ID do you need to fly to Lambert-St Louis Airport?
The necessary travel and health documents for your Lambert-St Louis Airport trip may vary depending on your travel plans and individual circumstances. Generally, you should have various documents, such as a national ID card or driver's license and a passport that is valid for six months beyond your scheduled arrival date. We recommend seeking advice from your airline or a trusted third party, such as IATA.
What is the most popular airline from Ontario to St. Louis?
momondo data reveals that the most frequently booked airline on the route from Ontario to St. Louis is Frontier, representing 44% of all bookings. The subsequent popular airlines are American Airlines at 23%, Southwest at 19%, and Delta at 8%.
Best airlines flying from Ontario to St. Louis
Compare and see reviews for airlines that fly from Ontario to St. Louis with momondo
| Airline | Rating | Free Cancellation | Price | ||
|---|---|---|---|---|---|
| PriceFrom $130 | Free Cancellation | Rating 5.9 3,295 reviews | |||
| PriceFrom $306 | Free Cancellation | Rating 7.2 10,000 reviews | |||
| PriceFrom $311 | Free Cancellation | Rating 8.0 7,946 reviews | |||
| PriceFrom $316 | Free Cancellation | Rating 7.4 8,790 reviews | |||
| PriceFrom $340 | Free Cancellation | Rating 8.0 4,287 reviews |
Traveling to a place near St. Louis?
Book flights to St. Louis if you plan to visit one of these locationsWhy use momondo?
Why should I use momondo to find a flight deal from Ontario to St. Louis?
momondo collates all your flight options in one place and lets you filter them to find the perfect flight from Ontario to St. Louis. momondo saves you time and could save you money on your trip.
Can I find flights from Ontario to St. Louis with flexible booking policies on momondo?
Yes. momondo allows you to filter the results for Ontario to St. Louis flights to just show those with flexible booking policies.
How can momondo help me find flights from Ontario to St. Louis?
Once all potential Ontario to St. Louis flight options are in front of you, momondo lets you sort and filter flights based on preferences such as airline, price and flight times amongst many other options.
I’m not ready to book a flight from Ontario to St. Louis right now. Can momondo alert me if prices change?
If you are not ready to book a flight from Ontario to St. Louis now, use our insights above to find helpful tips or alternatively set up a price alert, where momondo will track prices on flights to St. Louis and let you know when they change.