Cannon Ball is a census-designated place (CDP) on the Standing Rock Indian Reservation and in Sioux County, North Dakota, United States. It is located in the northeastern part of Sioux County, having developed at the confluence of the Cannonball River and Lake Oahe of the Missouri River. The population was 875 at the 2010 census.

The Standing Rock Reservation lies across the border between North and South Dakota in the United States, and is inhabited by ethnic "Hunkpapa and Sihasapa bands of Lakota Oyate and the Ihunktuwona and Pabaksa bands of the Dakota Oyate," as well as the Hunkpatina Dakota. The Ihanktonwana Dakota are the Upper Yanktonai, part of the collective of Wiciyena. The sixth-largest Native American reservation in land area in the US, Standing Rock includes all of Sioux County, North Dakota, and all of Corson County, South Dakota, plus slivers of northern Dewey and Ziebach counties in South Dakota, along their northern county lines at Highway 20.