Description Established as the Pine Ridge Agency in southwestern South Dakota between Nebraska and the Black Hills in 1878, Pine Ridge became a reservation in 1889. The second-largest reservation in the country, comprised of almost 2 million acres, it is home to 38,000 residents, almost 18,000 of whom are enrolled members of the Oglala Sioux Tribe. The history of the Pine Ridge Reservation is laden with both an awe-inspiring cultural heritage and the tragic effects of forced settlement on the reservation.