Clarkston is a city in Asotin County in the southeastern part of the State of Washington. It is part of the Lewiston ID-WA Metropolitan Statistical Area. The population was 7,229 in 2010 census.Walla Walla Community College opened a Branch Campus in Clarkston that serves the surrounding area, Lewiston, Idaho. It is still a major draw for the surrounding area.With a ZIP code of 99403, Clarkston has the highest zip code of any area in the contiguous United States.