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 at Chehalis, and its largest city is Centralia. The county is named after Meriwether Lewis. Lewis County is known for sharing many characteristics with eastern Washington instead of western Washington, where it is located, especially politically. Lewis County was created on December 19, 1845, by the provisional government of Oregon Territory.