The terrain of Keith County consists of low rolling hills. The level areas are used for agriculture, mainly in the lower part of the county. The North Platte River flows eastward into the northwest end of the county, feeding Lake McConaughy, then exiting the county's east line near its midpoint. The South Platte River flows eastward into the southwest end of the county, and crosses the lower central part of the county before exiting to the east, headed for its junction with the North Platte River well to the east of Keith County.