There are 14 US Post Offices in Lawrence County serving a total of 120,547 residents equating to 8,611 residents per post office. It's estimated that approximately 192,406 packages are handled across the 14 county post offices annually. Lawrence County is a county located in the U.S. state of Pennsylvania, United States. As of the 2010 census, the population was 91,108. The county seat is New Castle. Lawrence County makes up the entire New Castle, PA Micropolitan Statistical Area, which is also included in the Pittsburgh-New Castle-Weirton, PA-OH-WV Combined Statistical Area."