DeKalb County is a county located in the U.S. state of Tennessee. As of the 2020 census, the population was 20,080. Its county seat is Smithville. The county was created by the General Assembly of Tennessee on December 2, 1837, and was named for Revolutionary War hero Major General Johann de Kalb.

Smithville is a city in DeKalb County, Tennessee, United States. The population was 5,004 at the 2020 census, up from 3,994 at the 2010 census. It is the county seat of DeKalb County. Smithville is home to the Smithville Fiddler's Jamboree, which it has hosted annually since 1972.