Union County is a county located in the U.S. state of Tennessee. As of the 2020 census, its population was 19,802. Its county seat is Maynardville. Union County is included in the Knoxville metropolitan statistical area.

Maynardville is a city in and the county seat of Union County, Tennessee, United States. The city was named to honor Horace Maynard, who successfully defended the creation of Union County from a challenge from Knox County. Its population was 2,413 at the 2010 census, up from 1,782 at the 2000 census. It is included in the Knoxville metropolitan statistical area.