There are 7 US Post Offices in Linn County serving a total of 9,721 residents equating to 1,389 residents per post office. It's estimated that approximately 15,516 packages are handled across the 7 county post offices annually. Linn County (county code LN) is a county located in east-central Kansas. As of the 2010 census, the county population was 9,656. Its county seat is Mound City, and its most populous city is Pleasanton. The county was named for Lewis F. Linn, a U.S. Senator from Missouri."