Fenn is an unincorporated community in Idaho County, Idaho, United States. It is located on U.S. Route 95 on the Camas Prairie, 7 miles (11 km) northwest of Grangeville and 8 miles (13 km) south of Cottonwood. Fenn has a post office with ZIP code 83531.
Originally Tharp, it was named in 1915 (or earlier) after the Fenn family. Stephen S. Fenn (1820–92) arrived in Florence from California in 1862 with his wife and four children. He was an early settler, attorney, administrator, speaker of territorial legislature, and a territorial delegate to Congress. His son, Major Frank A. Fenn (1853–1927), also of many professions, was the speaker of the first state legislature. Frank's son Lloyd (1884–1953) also served in the legislature.
An earlier settlement a few miles north, Denver, was mostly abandoned after the Camas Prairie Railroad bypassed it. A grain elevator was constructed in Fenn in 1918, served by the railroad until the abandonment of its Second Subdivision line to Grangeville in late 2000.