Sullivan is Tennessee's second-oldest county;[4] it was established in 1779 when the area was still part of North Carolina.

[8] The western portion of the county lies within the Ridge-and-Valley Appalachians, which are characterized by long, narrow ridges roughly oriented northeast-to-southwest.

The northeastern end of Bays Mountain, part of the Ridge-and-Valley range, rises southwest of Kingsport.

The North Fork Holston forms part of Sullivan's boundary with Hawkins County to the west.

[10][11] Morrell Cave is located on the south side of the Holston River, 2.5 miles (4.0 km) east of Bluff City.

During the Civil War, the cave was a major source of saltpeter, the main ingredient of gunpowder.

Significant evidence of this mining activity remains in the cave, including evidence of large amounts of saltpeter-bearing dirt having been removed, pick marks in the dirt, and an elaborate system of trails used by the miners.

Cave historian Marion O. Smith has determined that two companies of the Confederate Nitre and Mining Bureau, District No.

[12] As of the 2020 United States census, there were 158,163 people, 68,560 households, and 44,284 families residing in the county.

The last Democratic presidential candidate to carry Sullivan County was southerner Jimmy Carter in 1976.

Angie Stanley retired from her seat in District 7 to unsuccessfully challenge incumbent mayor Richard Veneable in a primary.

Most races were uncontested (the republicans were the only ones on the ballot), except District 7 in which Lori Love (wife of perennial candidate Avril Love, and Democratic State Executive Committeewoman) garnered 15% of the vote, and District 9, Independent Candidate Randall Bowers garnered 15% if the vote.

Sullivan County Sherriff Jeff Cassidy first ran for the position in 2018 as an independent beating out controversial Republican Wayne Anderson.

Alongside Circuit Court Judge District 2, Part I, John S. McLellan III, who was serving as a Democrat, by changing both of their political affiliations to Republican in this election, they have effectively ended The election for County Mayor was between incumbent Richard S. Veneable (Republican), Val Edwards George (Independent [Conservative]), and Bobby Weaver (Independent [Conservative]) The Sullivan County Sheriffs Office has a staff of 260 deputies, corrections officers, and support personnel.

[27] A 2022 lawsuit claims that sheriff's deputies retaliated against a woman who had asked them to wear face masks due to the COVID-19 pandemic.