Lewis County is a county in the U.S. state of Washington. As of the 2020 census, the county's population was 82,149. The county seat is Chehalis, and its largest city is Centralia. Lewis County comprises the Centralia, WA Micropolitan Statistical Area, which is also included in the Seattle-Tacoma, WA Combined Statistical Area.

Centralia is a city in Lewis County, Washington, United States. It is located along Interstate 5 near the midpoint between Seattle and Portland, Oregon. The city had a population of 18,183 at the 2020 census. Centralia is twinned with Chehalis, located to the south near the confluence of the Chehalis and Newaukum rivers.