There are 54 US Post Offices in Plymouth County serving a total of 663,706 residents equating to 12,291 residents per post office. It's estimated that approximately 1,059,349 packages are handled across the 54 county post offices annually. Plymouth County is a county located in the U.S. state of Massachusetts. As of the 2010 census, the population was 494,919. Its county seats are Plymouth and Brockton. In 1685 the County was created by the Plymouth General Court, the legislature of Plymouth Colony, predating its annexation by the Massachusetts Bay Colony. Plymouth County is included in the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area.