Cheapest return flights from St. Louis to Denver in September from $117

AirHint found the following cheapest return flights from St. Louis (STL) to Denver (DEN) in September 2025 (see full year).

Return flights

27 Sep - 28 Sep Frontier Airlines direct
26 Sep - 28 Sep Frontier Airlines direct
25 Sep - 28 Sep Frontier Airlines direct
25 Sep - 29 Sep Frontier Airlines direct
26 Sep - 29 Sep Frontier Airlines direct
23 Sep - 27 Sep Frontier Airlines direct
20 Sep - 25 Sep Frontier Airlines direct
20 Sep - 24 Sep Frontier Airlines direct
17 Sep - 24 Sep Frontier Airlines direct
21 Sep - 25 Sep Frontier Airlines
12 Sep - 10 Oct Frontier Airlines
12 Sep - 10 Oct Frontier Airlines direct

Also check the deals for one-way flights from St. Louis to Denver in September.

Skyscanner

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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