Flathead County has a total area of 13,614 sq. km (5,256 sq. mi). Water comprises 3.01% of the total.

The Flathead Valley encompasses a large region of the county. It spans about 40 miles north of Flathead Lake and is bordered on the east by the majestic peaks of Glacier National Park. On the west, Flathead Valley is bordered by the evergreen-covered Salish Mountains. Between the lofty mountains to the east and west, flows the winding Flathead River. The entire Flathead Valley area is supported by 3 regional centers that are located within 15 miles of each other: Kalispell, Whitefish, and Columbia Falls.

Major cities include: Bigfork, Columbia Falls, Coram, Evergreen, Hungry Horse, Kalispell, Lakeside, Martin City, Niarada, Somers and Whitefish.