Lewis County is a county located in the U.S. state of Washington. As of the 2010 census, the population was 75,455. The county seat is Chehalis, and its largest city is Centralia. The county was created on December 19, 1845, by the Provisional Government of Oregon, and originally named after George Vancouver. In 1849 the county was renamed after Meriwether Lewis. Lewis County comprises the Centralia, WA Micropolitan Statistical Area, which is also included in the Seattle-Tacoma, WA Combined Statistical Area.