There are 12 US Post Offices in Mifflin County serving a total of 52,320 residents equating to 4,360 residents per post office. It's estimated that approximately 83,509 packages are handled across the 12 county post offices annually. Mifflin County is a county located in the U.S. state of Pennsylvania. As of the 2010 census, the population was 46,682. Its county seat is Lewistown. The county was created on September 19, 1789, from parts of Cumberland County and Northumberland County and named after Thomas Mifflin, the first Governor of Pennsylvania. Mifflin County comprises the Lewistown, PA Micropolitan Statistical Area."