There are 21 US Post Offices in Dauphin County serving a total of 198,288 residents equating to 9,442 residents per post office. It's estimated that approximately 316,490 packages are handled across the 21 county post offices annually. Dauphin County /\u02c8d\u0254\u02d0f\u026an/ is a county in the U.S. state of Pennsylvania. As of the 2010 census, the population was 268,100. The county seat and the largest city is Harrisburg, Pennsylvania's state capital and tenth largest city. The county was created/\"erected\" on March 4, 1785, from part of Lancaster County and was named after Louis-Joseph, Dauphin of France, the first son of Louis XVI. Dauphin County is included in the Harrisburg-Carlisle, PA Metropolitan Statistical Area. Located within the county is Three Mile Island Nuclear Generating Station, site of the 1979 nuclear core meltdown.