There are 5 US Post Offices in Riley County serving a total of 48,730 residents equating to 9,746 residents per post office. It's estimated that approximately 77,779 packages are handled across the 5 county post offices annually. Riley County (standard abbreviation: RL) is a county located in the U.S. state of Kansas. As of the 2010 census, the population was 71,115. The largest city and county seat is Manhattan. Riley County is home to two of Kansas' largest employers: Fort Riley and Kansas State University. Among notable current and former residents of Riley County are former Governor John W. Carlin, General Glen Edgerton and millionaire miner Horace A. W. Tabor."