There are 8 US Post Offices in Williamson County serving a total of 183,901 residents equating to 22,988 residents per post office. It's estimated that approximately 293,527 packages are handled across the 8 county post offices annually. Williamson County is a county in the U.S. state of Tennessee. As of the United States Census, the population was 205,226. The county seat is Franklin. The county is named after Hugh Williamson, a North Carolina politician who signed the U.S. Constitution. Williamson County is part of the Nashville-Davidson-Murfreesboro-Franklin, TN Metropolitan Statistical Area."