There are 11 US Post Offices in Marshall County serving a total of 10,285 residents equating to 935 residents per post office. It's estimated that approximately 16,416 packages are handled across the 11 county post offices annually. Marshall County (standard abbreviation: MS) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 10,117. The largest city and county seat is Marysville."