Hermiston is a city in Umatilla County, Oregon, United States. Its population of 20,322 makes it the largest city in Eastern Oregon. Hermiston is the largest and fastest-growing city in the Hermiston-Pendleton Micropolitan Statistical Area, the eighth largest Core Based Statistical Area in Oregon with a combined population of 92,261 at the 2020 census. Hermiston sits near the junction of I-82 and I-84, and is 7 miles south of the Columbia River, Lake Wallula, and the McNary Dam. The Hermiston area has become a hub for logistics and data center activity due to the proximity of the I-82 and I-84 interchange, Pacific Northwest fiber optic backbone, and low power costs.

Umatilla County is one of the 36 counties in the U.S. state of Oregon. The population of 81,826 ranks it as the 14th largest in Oregon, and largest in Eastern Oregon. Hermiston is the largest city in Umatilla County, but Pendleton remains the county seat. Umatilla County is part of the Hermiston-Pendleton, OR Micropolitan Statistical Area, which has a combined population of 94,833. It is included in the eight-county definition of Eastern Oregon.