Grand River National Grassland is a National Grassland in northwestern South Dakota, USA. It is named for the Grand River. The North and South forks of the rivers meet in the grassland. It has a land area of 154,783 acres (241.85 sq mi, or 626.38 km²). In descending order of acreage it lies in parts of Perkins, Corson, and Ziebach counties. The portion in Corson County also lies within the Standing Rock Indian Reservation. The portion in Ziebach County also lies within the Cheyenne River Indian Reservation. The grassland is administered by the USDA-Forest Service as part of the Dakota Prairie Grasslands (DPG) from offices in Bismarck, North Dakota. There is a local Ranger District office (shared with Cedar River National Grassland) in Lemmon, South Dakota. The DPG is part of Region One of the Forest Service. The Regional Headquarters is in Missoula, MT.