Pasco ( PAS-koh) is a city in, and the county seat of, Franklin County, Washington, United States. It had a population of 59,781 at the 2010 census, and 75,432 as of the July 1, 2019 Census Bureau estimate.
Pasco is one of three cities (the others being Kennewick and Richland) that make up Washington state's Tri-Cities region, a mid-sized metropolitan area of approximately 296,224 people.
On October 16, 1805, the Lewis and Clark Expedition camped in the Pasco area, at a site now commemorated by Sacajawea State Park. The area was frequented by fur trappers and gold traders. In the 1880s, the Northern Pacific Railway was built near the Columbia River, bringing many settlers to the area. Pasco was officially incorporated on September 3, 1891. It was named by Virgil Bogue, a construction engineer for the Northern Pacific Railway after Cerro de Pasco, a city in the Peruvian Andes, where he had helped build a railroad. In its early years Pasco was a small railroad town, but the completion of the Grand Coulee Dam in 1941 brought irrigation and agriculture to the area.
Due in large part to the presence of the Hanford Site (which made the plutonium for the Nagasaki atomic bomb), the entire Tri-Cities area grew rapidly from the 1940s through 1950s. However, most of the population influx resided in Richland and Kennewick, as Pasco remained primarily driven by the agricultural industry, and to a lesser degree the NP Pasco rail yards.