There are 7 US Post Offices in Doniphan County serving a total of 7,806 residents equating to 1,115 residents per post office. It's estimated that approximately 12,459 packages are handled across the 7 county post offices annually. Doniphan County (county code DP) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 7,945. Its county seat is Troy, and its most populous city is Wathena."