- Pasco is a city located in Franklin County, Washington, United States. It is the fourth-largest city in the Tri-Cities area, which also includes Kennewick and Richland. The city's population was estimated to be around 75,432 in 2019. Pasco is known for its agricultural industry, as well as being a transportation hub due to its location along the Columbia River and Interstate 182. It is also home to the Eastern Washington State Historical Society Museum and the Franklin County Historical Museum.