Foothills County was originally formed as the Municipal District (MD) of Sheep River No. 31 on January 1, 1954 through the amalgamation of portions of Improvement District No. 46 and the MDs of Highwood No. 31, Turner Valley No. 32, and Springbank No. 45. Its name was changed to the MD of Foothills No. 31 shortly thereafter on March 25, 1954. Foothills County assumed its present name on January 1, 2019.

In the 2021 Census of Population conducted by Statistics Canada, Foothills County recorded a population of 23,199 living in 8,450 of its 9,075 total private dwellings, a change of 2.6% from its 2016 population of 22,616. With a land area of 3,604.76 km2 (1,391.81 sq mi), it had a population density of 6.4/km2 (16.7/sq mi) in 2021.

In the 2016 Census of Population conducted by Statistics Canada, the Foothills County recorded a population of 22,766 living in 8,156 of its 8,689 total private dwellings, a 7.1% change from its 2011 population of 21,248. With a land area of 3,636.8 km2 (1,404.2 sq mi), it had a population density of 6.3/km2 (16.2/sq mi) in 2016.