There are 10 US Post Offices in Washington County serving a total of 51,293 residents equating to 5,129 residents per post office. It's estimated that approximately 81,869 packages are handled across the 10 county post offices annually. Washington County is a county located in the U.S. state of Mississippi. As of the 2010 census, the population was 51,137. Its county seat is Greenville. The county is named in honor of the first President of the United States, George Washington. The Greenville, MS Micropolitan Statistical Area includes all of Washington County. It is located in the Mississippi Delta."