High Quality Content by WIKIPEDIA articles! The Flathead Indian Reservation, located in western Montana on the Flathead River, is home to the Bitterroot Salish, Kootenai, and Pend d`Oreilles Tribes - also known as the Confederated Salish and Kootenai Tribes of the Flathead Nation. The reservation was created through the July 16, 1855, Treaty of Hellgate and includes parts of four Montana counties: Lake, Sanders, Missoula, and Flathead. The Flathead Indian Reservation is an area of 1,938 square miles (5,020 km2) (1,317,000 acres (533,000 ha)) of forested mountains and valleys just west of the Continental Divide.