Blountville is a census-designated place in and the county seat of Sullivan County, Tennessee, United States. The population was 3,074 at the 2010 census. It is the only Tennessee county seat not to be an incorporated city or town.Blountville is part of the Kingsport?Bristol?Bristol 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.