According to the U.S. Census Bureau, the county has a total area of , of which is land and (2.0%) is water. It is the third-smallest county in Oklahoma by land area and second-smallest by total area. The county's northern section lies in the Sandstone Hills physiographic region and is suitable for farming, while the southern portion is in the Arbuckle Mountains region, which is dominated by rolling hills and rock outcrops. The Washita River drains the county. Chickasaw National Recreation Area (CNRA) lies in the county. Lake of the Arbuckles, part of CNRA, was completed on Rock Creek in 1966.