Franklin County is a county located in the U.S. state of Washington. As of the 2020 census, its population was 96,749. The county seat and most populous city is Pasco. The county was formed out of Whitman County on November 28, 1883, and is named for Benjamin Franklin. Franklin County is included in the Tri-Cities metropolitan area. Together, Kennewick, Richland and Pasco comprise Washington's Tri-Cities.