There are 17 US Post Offices in Cumberland County serving a total of 222,002 residents equating to 13,059 residents per post office. It's estimated that approximately 354,340 packages are handled across the 17 county post offices annually. Cumberland County is a county located in the U.S. state of Pennsylvania. As of the 2010 census, the population was 235,406. Its county seat is Carlisle. Cumberland County is included in the Harrisburg-Carlisle, PA Metropolitan Statistical Area."