There are 3 US Post Offices in Washington County serving a total of 13,187 residents equating to 4,396 residents per post office. It's estimated that approximately 21,048 packages are handled across the 3 county post offices annually. Washington County is a county located in the U.S. state of North Carolina. As of the 2010 census, the population was 13,228. Its county seat is Plymouth. The county was formed in 1799 from the western third of Tyrrell County. It was named for George Washington."