There are 15 US Post Offices in Washington County serving a total of 218,602 residents equating to 14,573 residents per post office. It's estimated that approximately 348,913 packages are handled across the 15 county post offices annually. Washington County is a county located in the U.S. state of Minnesota. As of the 2010 census, the population was 238,136, making it the fifth-most populous county in Minnesota. Its county seat is Stillwater. The county was established in 1849. Washington County is included in the Minneapolis-St. Paul-Bloomington, MN-WI Metropolitan Statistical Area."