Butler County is a county in the U.S. state of Kansas and is the largest county in the state by total area. Its county seat is El Dorado and its most populous city is Andover. As of the 2020 census, the county population was 67,380. The county was named for Andrew Butler, a U.S. Senator from South Carolina who coauthored the Kansas–Nebraska Act.

Kansas is a landlocked state in the Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named after the Kansas River, in turn named after the Kansa people. Its capital is Topeka, and its most populous city is Wichita, however the largest urban area is the bi-state Kansas City, MO–KS metropolitan area.