High Quality Content by WIKIPEDIA articles! Walnut Hill is a census-designated place (CDP) in Sullivan County, Tennessee, United States. The population was 2,756 at the 2000 census. It is part of the Kingsport Bristol (TN) Bristol (VA) 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.