Two rivers meet at Clay County's northern edge

Clay County's northern edge is water. The Red River forms the boundary, and the Wichita River crosses northwestern Clay County before joining the Red just west of the Byers bend. Turkey Creek, Dry Fork, Hay Creek, and East Post Oak Creek break up land that is otherwise nearly level or gently sloping.

Much of the county sits in Cross Timbers and prairie country, with grasses, mesquite, blackjack oak, post oak, and elm. The northwest corner reaches into the Rolling Plains, where gently rolling rangeland is cut by streams flowing east toward the Cross Timbers and Prairies.

Clay County is a transition rather than one uniform landscape. Farm ground and open range share the map with wooded stream edges, while the Wichita and Red rivers meet along the county's north side.