A more thorough explanation:

Definition: Indian country refers to the land within the borders of all Indian reservations, the land occupied by an Indian community (whether or not located within a recognized reservation), and any land held in trust by the United States but beneficially owned by an Indian or tribe. It can also refer to any region, especially during the U.S. westward migration, where a person was likely to encounter Indians.

• The Navajo Nation reservation in Arizona, New Mexico, and Utah is considered Indian country.
• The Standing Rock Sioux Tribe's land in North Dakota is also Indian country.
• During the westward expansion of the United States, pioneers traveling through the Great Plains and Rocky Mountains were likely to encounter Indian tribes, making those regions Indian country.

The examples illustrate how Indian country can refer to specific areas of land that are either owned by or occupied by Native American tribes. It can also refer to historical regions where Native Americans were present and encountered by non-Native Americans.