Unicoi County is a county located in the U.S. state of Tennessee. As of the 2020 census, the population was 17,928. Its county seat is Erwin. Unicoi is a Cherokee word meaning "white," "hazy," "fog-like," or "fog draped," and refers to the mist often seen in the foothills and mountains of this far northeast county. Unicoi County is part of the Johnson City Metropolitan Statistical Area, which is a component of the Johnson City–Kingsport–Bristol, TN-VA Combined Statistical Area, commonly known as the "Tri-Cities" region.

Erwin is a town in and the county seat of Unicoi County, Tennessee, United States. The population was 6,097 at the 2010 census. It is part of the Johnson City metropolitan area, which is a component of the "Tri-Cities" region.