According to archeological evidence, Native Americans first arrived in the Glacier area some 10,000 years ago. The earliest occupants with lineage to current tribes were the Salish, Flathead, Shoshone and Cheyenne. The Blackfeet arrived around the beginning of the 18th century and soon dominated the eastern slopes of what later became the park, as well as the Great Plains immediately to the east. The park region provided the Blackfeet shelter from the harsh winter winds of the plains, and supplemented their traditional bison hunts with other game meat.
Today, the Blackfeet Indian Reservation borders the park in the east, while the Flathead Indian Reservation is located west and south of the park. When the Blackfeet Reservation was first established in 1855 by the Lame Bull Treaty, it included the eastern area of the current park up to the Continental Divide. To the Blackfeet, the mountains of this area, especially Chief Mountain and the region in the southeast at Two Medicine, were considered the "Backbone of the World" and were frequented during vision quests. In 1895, Chief White Calf of the Blackfeet authorized the sale of the mountain area, some 800,000 acres (3,200 kmē), to the U.S. government for $1.5 million. This established the current boundary between the park and the reservation.