History Of Umatilla County Umatilla County was created on September 27, 1862, out of a portion of Wasco County. Umatilla is an Indian term meaning "rippling water" or "water rippling over sand" and has provided the name both for the county and its major river. Adjustments were made to the county's boundaries following the creation of Grant, Morrow, Union, and Wallowa Counties. The county...