Peltier was born on September 12, 1944,[17] at the Turtle Mountain Indian Reservation of the Turtle Mountain Chippewa near Belcourt, North Dakota, in a family of 13 children.[18] Peltier's parents divorced when he was four years old.[19] Leonard and his sister Betty Ann lived with their paternal grandparents Alex and Mary Dubois-Peltier in the Turtle Mountain Indian Reservation.[8] In September 1953, at the age of nine, Leonard was enrolled at the Wahpeton Indian School in Wahpeton, North Dakota, an Indian boarding school run by the Bureau of Indian Affairs (BIA).[19] Leonard remained 150 miles (240 km) away from his home at Wahpeton Indian School through the ninth grade; the school forced assimilation to white American culture by requiring the children to use English and forbidding the inclusion of Native American culture.[20] He graduated from Wahpeton in May 1957, and attended the Flandreau Indian School in Flandreau, South Dakota.[21] After finishing the ninth grade, he returned to the Turtle Mountain Reservation to live with his father.[21] Peltier later obtained a general equivalency degree (GED).[20]