There are 7 US Post Offices in Martin County serving a total of 24,788 residents equating to 3,541 residents per post office. It's estimated that approximately 39,564 packages are handled across the 7 county post offices annually. Martin County is a county located in the U.S. state of North Carolina. As of the 2010 census, the population was 24,505. Its county seat is Williamston.