There are 12 US Post Offices in Cass County serving a total of 97,503 residents equating to 8,125 residents per post office. It's estimated that approximately 155,626 packages are handled across the 12 county post offices annually. Cass County is a county located in the western part of the U.S. state of Missouri. As of the 2010 census, the population was 99,478. Its county seat is Harrisonville. The county was organized in 1835 as Van Buren County but was renamed in 1849 after U.S. Senator Lewis Cass of Michigan who later became a presidential candidate. Cass County is part of the Kansas City, Missouri Metropolitan Statistical Area."