Hermiston () is a city in Umatilla County, Oregon, United States. Its population of 18,200 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 87,062 at the 2010 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. The city is also known for its watermelons, which are part of its branding.
The historic inhabitants of the area were the indigenous Umatilla, Cayuse, Walla Walla, and Columbia Indians, descendants of peoples who lived in this area for thousands of years. The earliest European settlers were Catholic missionaries who established a mission near Pendleton in 1847. The territorial government organized Umatilla County in 1862 from the larger Wasco County. On July 10, 1907, the town of Hermiston was incorporated. Robert Louis Stevenson's novel Weir of Hermiston inspired the name.