There are 16 US Post Offices in Knox County serving a total of 356,305 residents equating to 22,269 residents per post office. It's estimated that approximately 568,703 packages are handled across the 16 county post offices annually. Knox County is a county in the U.S. state of Tennessee. As of the 2010 census, the population was 432,226, making it the third-most populous county in Tennessee. Its county seat is Knoxville, the third-most populous city in Tennessee. Knox County is included in the Knoxville, TN Metropolitan Statistical Area. The county is at the geographical center of the Great Valley of East Tennessee. Near the heart of the county is the origin of the Tennessee River at the union of the Holston and French Broad rivers."