Hermiston is located in Umatilla County, Oregon, near the junction of I-82 and I-84. U.S. Route 395 also goes through the center of the city. Hermiston is seven miles south of the Columbia River, Lake Wallula, and the McNary Dam. The Umatilla Chemical Depot and the Umatilla Chemical Agent Disposal Facility are five miles west of the city, northeast of the intersection of I-84 and I-82. As of 2010, the estimated population was 16,745 residents.
Hermiston is the larger of the two principal cities of the Pendleton-Hermiston Micropolitan Statistical Area, a micropolitan area that covers Morrow and Umatilla counties and had a combined population of 87,062 at the 2010 census.