Riley County (standard abbreviation: RL) is a county located in the U.S. state of Kansas. The county's population was 71,115 for the 2010 census. The largest city and county seat is Manhattan. The county is part of the Manhattan, Kansas, Metropolitan Statistical Area.
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.
Riley County, named for Mexican-American War general Bennet Riley, was on the western edge of the 33 original counties established by the Kansas Territorial Legislature in August 1855. For organizational purposes, Riley County initially had attached to it Geary County and all land west of Riley County, across Kansas Territory into present-day Colorado.
The first Territorial Capital of Kansas Territory was located in the boundaries of Riley County, in the former town of Pawnee. The site now falls within the boundaries of Fort Riley, a U.S. Army post.
Manhattan was selected as county seat in contentious fashion. In late 1857, an election was held to select the county seat, with Ogden prevailing. However, Manhattanites suspected election fraud, and were eventually able to prove that a number of votes were illegally cast. Sheriff David A. Butterfield was forced to secure the county's books and records for Manhattan, and Manhattan was finally officially declared the county seat in 1858.
On May 30, 1879, the "Irving, Kansas Tornado" began in Riley County. This tornado is estimated to have been an F4 on the Fujita scale, with a damage path wide and long. Eighteen people were killed and sixty were injured.