Smithville is a city in DeKalb County, Tennessee, United States. The population was 3,994 at the 2000 census. It is the county seat of De Kalb County.
Smithville is located at 35°57′26″N 85°49′15″W / 35.95722°N 85.82083°W / 35.95722; -85.82083 (35.957191, -85.820756), approximately 25 miles west of Cookeville and 70 miles east of Nashville.
According to the United States Census Bureau, the city has a total area of 5.9 square miles (15.2 km²), all of it land.