There are 11 US Post Offices in Marion County serving a total of 12,360 residents equating to 1,124 residents per post office. It's estimated that approximately 19,728 packages are handled across the 11 county post offices annually. Marion County (standard abbreviation: MN) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 12,660. The county seat is Marion. The county was named in honor of Francis Marion, a Brigadier General of the American Revolutionary War, known as the \"Swamp Fox\"."