Clarkston is a city in Asotin County, Washington, United States. It is part of the Lewiston, ID-WA metropolitan area, and is located west of Lewiston, Idaho, across the Snake River. The population of Clarkston was 7,161 at the 2020 census. Walla Walla Community College opened a branch campus in Clarkston that serves the surrounding area. Clarkston's ZIP code, 99403, is the highest numerically in the contiguous United States.