There are 7 US Post Offices in Leavenworth County serving a total of 70,850 residents equating to 10,121 residents per post office. It's estimated that approximately 113,085 packages are handled across the 7 county post offices annually. Leavenworth County (county code LV) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 76,227. Its county seat and most populous city is Leavenworth."