Clark County is a county located in the southwestern part of the U.S. state of Washington, across the Columbia River from Portland, Oregon.
Clark County was the first county of Washington, named after William Clark of the Lewis and Clark Expedition. It was created by the provisional government of Oregon Territory on August 20, 1845, and at that time covered the entire present-day state.
On July 1, 2011 Estimate, Clark County's population was to be 433,418. Its county seat is at Vancouver, which is also its largest city.