Marshall County is a county located in the U.S. state of Tennessee. As of the 2020 census, the population was 34,318. Its county seat is Lewisburg. Marshall County comprises the Lewisburg Micropolitan Statistical Area, which is also included in the Nashville-Davidson–Murfreesboro–Franklin, TN Metropolitan Statistical Area. It is in Middle Tennessee, one of the three Grand Divisions of the state. The Tennessee Walking Horse Breeders' and Exhibitors' Association is based here.