Blacktail Deer Creek is a tributary of the Beaverhead River, approximately 38 miles (61 km) long, in southwest Montana, United States. It rises in the Beaverhead National Forest in the Snowcrest Range in southern Beaverhead County. It flows northwest, joining the Beaverhead River near Dillon, Montana. The creek contains rainbow, brook and brown trout as well as mountain whitefish, longnose sucker, longnose dace and mottled sculpin. On August 7–8, 1863, a group of 28 prospectors embarked from the mouth of Blacktail Deer Creek to prospect for gold in the upper Snake River in Idaho Territory.