Cheap flights from St. Louis to Illinois from $58

The cheapest month to fly to Illinois from St. Louis is in December. Flight prices, which tend to average around $328, are often lower during this time because this is during the off-season. If you aren’t able to travel to Illinois during the month of December, then flying in August is also cheap. Prices for this month can be found on momondo for an average of $332.

The cheapest day to depart from St. Louis to Illinois is on a Friday when prices can be found for as low as $646. Flights from St. Louis to Illinois on a Saturday will generally be more expensive and average around $881. Keep in mind that these prices on both days could fluctuate depending on the season and the demand.

Our most recent data shows that the best time of day to fly to Illinois is in the morning. Flights from St. Louis to Illinois during this time can be as low as $578. Flights at noon are often more expensive with an average ticket price of $1,144.

Fly from Lambert-St Louis to Chicago Midway for the best Lambert-St Louis - Illinois flight prices

You are more likely to see cheaper flights to Illinois from St. Louis when booking weeks ahead of your departure date. In general, you can expect to find flights to Illinois for around $373 when searching weeks out. However, flight prices might be lower outside of this timeframe. For example, people recently found flights to Illinois from St. Louis for as low as $117 on momondo.

There are 4 cabin classes available to choose from on St. Louis to Illinois flights. Cabin price and availability will vary by airline so perform a search above to find the right deals for you.

Southwest, Frontier, and Delta are the most popular carriers operating from Lambert-St Louis to Illinois

United Airlines, Southwest and American Airlines are the top three most popular airlines that fly to Illinois from St. Louis according to our data. United Airlines is the first choice among our users, with 37% of people opting to fly with this airline when traveling to Illinois. Keep in mind that there are 4 different airlines that fly to Illinois on a routine basis, so you have a few additional options to choose from.

65 flights are operational daily from St. Louis to Illinois as of November 2026. The most popular departure time for this route is 1:00PM, with 51% of flights per day taking off at noon.

The number of flights available between St. Louis and Illinois is 457 per week as of November 2026. The most frequent departure day is Fri, with 16% of weekly flights leaving on this day.