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.