 No changes to counties have been made since the formation of Pend Oreille County in 1911, except when the small area of Cliffdell was moved from Kittitas to Yakima County in 1970.King County, home to the state's largest city, Seattle, holds 30% of Washington's population (2,252,782 residents of 7,614,893 in 2019) and has the highest population density with more than 1,000 people per square mile (400/km2).Garfield County is both the least populated (2,225) and least densely populated (3.1/mi2).