Organized in 1855, Butler County's seat is Eldorado. Butler County was named for Andrew P. Butler, who was United States Senator from South Carolina, from 1846 to 1857.

Butler County, Kansas is mostly rolling grass-covered hills with broad river valleys winding through them. Elevations range from 1625 feet on the east Flint Hills, down to 1148 feet in the Walnut River valley.

Petroleum production and refining is still the major factor in the county's economy. Farming and ranching are also important, and the state correctional facility and light industry are growing segments in Butler County.