Shawnee County is located in northeast Kansas, in the central United States. Its county seat and most populous city is Topeka, the state capital. As of the 2020 census, the population was 178,909, making it the third-most populous county in Kansas. The county was one of the original 33 counties created by the first territorial legislature in 1855, and it was n…Shawnee County is located in northeast Kansas, in the central United States. Its county seat and most populous city is Topeka, the state capital. As of the 2020 census, the population was 178,909, making it the third-most populous county in Kansas. The county was one of the original 33 counties created by the first territorial legislature in 1855, and it was named for the Shawnee tribe.