Umatilla Indians. A Shahaptian tribe formerly lining on Umatilla Reservation and the adjacent banks of the Columbia in Oregon. They were included under the Walla Walla by Lewis and Clark in 1805, though their language is distinct. In 1855 they joined in a treaty with the United States and settled on the Umatilla Reservation in eastern Oregon. They are said to number 250, but this figure is doubtful, owing to a mixture of tribes on the reservation.