The Umatilla are one of three tribes that make up the Confederated Tribes of the Umatilla Indian Reservation. The other two tribes are the Cayuse and the Walla Walla. This confederation was established by a treaty between the three tribes and the U.S. Government in 1855, and once consisted of more than 8,000 people (Tamástslikt). .
All three tribes have lived on the Columbia River Plateau for over 10,000 years (Tamástslikt). Today many tribal members of the confederation live on the Umatilla Indian Reservation near Pendleton, Oregon. However, prior to the treaty of 1855, these three tribes inhabited 6.4 million acres in Southeastern Washington, Northeastern Oregon and western Idaho. The major rivers of this area are the Columbia, Palouse, Snake, Yakima, Walla Walla, Umatilla, Grand Ronde and John Day, now known as their homeland. The Umatilla tribe spent most of their days on the Columbia River, the lower regions of its tributaries including the Umatilla River and Willow Creek (Miller).
The Plateau culture groups call themselves bands, instead of tribes. Each tribe was a large grouping of family bands, including one headman per band, and each band made its own decisions. The names Cayuse Tribe, Umatilla Tribe or Walla Walla Tribe came when the first explorer found several bands camping together in one spot. If the location was Umatilla, then all of the bands were called Umatillas' (UIR). .
The Umatilla tribe is part of a much larger culture group called the Plateau Culture. The Plateau Culture includes the Nez Perce bands of Idaho and Washington, the Yakima bands of Central Washington and the Wasco and Warm Springs bands of North Central Oregon on the lower Columbia River (UIR). The Umatilla spoke their own dialect called the original Cayuse language, which is almost extinct today. A few words are still spoken by a few individuals on the Umatilla Reservation (Kaag).