Rooks County (standard abbreviation: RO) is a county located in the U.S. state of Kansas. As of the 2020 census, the county population was 4,919. The county seat is Stockton, and the largest city is Plainville. The county was named for Private John C. Rooks of the 11th Kansas Infantry who died at the Battle of Prairie Grove near Fayetteville, Arkansas, during the Civil War.