The Great Sioux Nation is a general term sometimes applied to the Sioux generally or the Lakota specifically. It is also sometimes applied to a hypothetical state in the western and midwestern United States. It would occupy the following recognized Indian Reservations:

• Cheyenne River Reservation
• Crow Reservation
• Crow Creek Reservation
• Omaha Reservation
• North Cheyenne Reservation
• Pine Ridge Reservation
• Rosebud Reservation
• Santee Reservation
• Sisseton Reservation
• Standing Rock Reservation
• Winnebago Reservation
• Yankton Reservation

It also would include the defunct Great Sioux Reservation and other "unceded Indian territory " in four states. It therefore would occupy parts the following states:

• South Dakota
• Montana
• Nebraska
• North Dakota
• Wyoming

Therefore, the theoretical Great Sioux Nation occupies only parts of the United States where Sioux tribes have some legal claim with regard to treaties with the Federal government. It does not include the traditional Sioux homeland in the Carolinas. It also is heavily tilted in favor of the Lakota people. Only a fraction of land occupied by Dakota and Nakota tribes immediately before white settlement is included, while virtually all Lakota land is included.

Historically, the Great Sioux Nation and the United States have had a turbulent relationship. The last great Indian battles, the Battle of Little Big Horn and the Battle of Wounded Knee, were fought between these two peoples. However, the Sioux and Americans were previously closely allied. The Sioux played a critical part in the settling of the midwest and west. Sioux warriors with federal arms were successful in removing the Ojibwe and Mandan tribes from large parts of the country.