Prices were available within the past 7 days and start at $38 for one-way flights and $76 for round trip, for the period specified. Prices and availability are subject to change. Additional terms apply.
Prices were available within the past 7 days. Prices and availability are subject to change.
The most popular months for travelers to fly to O'Fallon are January, March, and April, when peak temperatures in O'Fallon can reach up to 55.8°F in April. If you prefer quieter travel, consider September, the least busy time to visit with temperatures around 70.2°F and typically the lowest average one-way fare (around $222), roughly 9% cheaper than the yearly average. Looking for additional cheaper months to fly? October, May, and August offer average one-way fares of around $230, making them good options for flexible travelers.
 Month |  Temperature |  Precipitation |  Cloudiness |  Demand |  Average one-way Fare |
| January | 31.6°F (-0.2°C) | Light Rain | Mostly Cloudy | Moderately High | $277 |
| February | 34.9°F (1.6°C) | Light Rain | Mostly Sunny | Average | $245 |
| March | 46.2°F (7.9°C) | Light Rain | Mostly Sunny | Moderately High | $273 |
| April | 55.8°F (13.2°C) | Light Rain | Mostly Sunny | Moderately High | $249 |
| May | 66.2°F (19.0°C) | Light Rain | Mostly Sunny | Average | $229 |
| June | 75.6°F (24.2°C) | Light Rain | Mostly Sunny | Average | $258 |
| July | 77.9°F (25.5°C) | Light Rain | Mostly Sunny | Average | $251 |
| August | 76.1°F (24.5°C) | Light Rain | Mostly Sunny | Average | $235 |
| September | 70.2°F (21.2°C) | Light Rain | Mostly Sunny | Moderately Low | $222 |
| October | 58.3°F (14.6°C) | Light Rain | Mostly Sunny | Average | $225 |
| November | 45.9°F (7.7°C) | Light Rain | Mostly Sunny | Moderately Low | $243 |
| December | 37.6°F (3.1°C) | Light Rain | Mostly Sunny | Moderately Low | $249 |
*Average one-way fare is based on Expedia flight booking data from January 2025 to April 2026 for the specified route and travel class and may change depending on availability, dates, and demand.
*Flight schedules are subject to change.
*Available to One Key members.
The cheapest day to fly
Get started finding a cheap flight to O'Fallon on Expedia by either choosing a deal on this page or entering into the search bar your travel dates, origin airport, and whether you want roundtrip or one-way airfare. You can filter for flexibility, number of stops, airline, and departure/arrival times to find the best flight for you.
The cheapest month to fly
July is the cheapest month to fly to O'Fallon. This coincides with the low season when fewer people travel. Whichever month you travel in, though, be sure to book at least a month in advance if you want to score cheap tickets to O'Fallon. ARC's data shows that domestic flights booked 28 days or more before departure are typically 24% cheaper than those booked last minute.
The most affordable time to book a flight
Typically, a Sunday can be the cheapest time to book a flight to O'Fallon, according to ARC’s data. On average, you could save between 6% and 13% by booking on a Sunday instead of a Friday, which is the most expensive day to make a reservation.
The cheapest round-trip tickets to O'Fallon
The lowest price for round-trip flights to O'Fallon in 2026 starts from from $76, while one-way tickets start from from $38. Expedia's effective search tool is one of the best ways to find a budget airfare. Simply enter your dates, and within seconds, it'll show you a vast selection of the cheapest flights to O'Fallon. If you have a preferred departure time or airline, you can use the handy filters to customize your search.
The cheapest airlines flying to O'Fallon
Frontier Airlines, Delta, Southwest Airlines, United, American Airlines are just some of the airlines that can typically offer cheap tickets to O'Fallon. You can find their most affordable flights by using the “airline” search filter and then sorting prices from low to high. As a trusted partner of the world's leading airlines, Expedia offers you some of the best airfare deals to O'Fallon and countless more destinations worldwide.
The most affordable airports to fly into
To view the cheapest airports to fly into for O'Fallon, simply order your search results from lowest to highest price. Expedia's search tool compares flight prices for all airports close to your destination, so you don't have to manually search them one by one to find the cheapest flight to O'Fallon. If you have a preferred place to fly into, take advantage of the “arrival airport” filter to narrow down your search on Expedia.
Save with a package
With Expedia's amazing package deals, you could save hundreds of dollars by booking your O'Fallon plane tickets together with your accommodations, car rental, or activities. Just select the search wizard's “package” option to view some of the cheapest deals. Look out for the green savings label to see how much you're saving.
Date flexibility for the cheapest flights to O'Fallon
If you can be flexible with your travel dates, it's a good idea to broaden your search by comparing prices on different days. This will open up more options, meaning you could uncover a less expensive flight to O'Fallon.
Stopover savings
The cheapest tickets to O'Fallon are sometimes those with a stopover. Book one of these flights, and you'll change planes at an airport en route to O'Fallon. While the overall travel time might be longer than a non-stop flight, you may decide it's worth it for the money saved.
Get Expedia's Price Drop Protection
Price Drop Protection means that if your flight gets cheaper after booking, you'll be credited the difference*. This gives you peace of mind that you're getting one of the cheapest flights to O'Fallon for your chosen departure. Expedia's Price Drop Protection is available for a small fee but is free to One Key Gold and Platinum tier members.
*Terms apply.
Use our Price Tracking feature
Expedia's Price Tracking feature is another great tool that removes the guesswork from finding cheap flights to O'Fallon. Simply download the free Expedia app to your smart device and activate O'Fallon flight price alerts for your travel dates. There's even a price predictor tool that uses historical data to indicate the best time to book, giving you peace of mind that you'll nab the lowest prices.
Book with Expedia
As well as Price Drop Protection and Price Tracking, Expedia's close partnership with a vast selection of the world's leading airlines means you're sure to find cheap flights to O'Fallon. Plus, the One Key rewards program lets you earn real cash rewards on most bookings that you can use to save money on future trips. Best of all, it's free to join, and members often unlock exclusive discounts, too.
Disclaimer: ARC The statistics are based on average round-trip ticket prices between January and August 2023. The percentages you see are averages.
Destination airport | Lambert-St. Louis Intl. |
|---|---|
Destination airport IATA code | STL |
Destination city name | St. Louis |
Roundtrip price | $76 |
Prices were available within the past 7 days and start at $38 for one-way flights and $76 for round trip, for the period specified. Prices and availability are subject to change. Additional terms apply.
