Lewis County is located in the southwest corner of Washington state. As of 2010, the population was 75,455.

The county seat is at Chehalis, and its largest city is Centralia. Other Lewis county communities include: Napavine, Adna, Pe Ell, Winlock, Toledo, Mossyrock, Onalaska, Morton, Randle, Vader Ethel,  and Packwood.

In addition there are several small communities in the outlying areas that are points of interest such as Doty, Mineral, Galvin and Cinebar.

The county is named after the explorer Meriwether Lewis.  Lewis County was created on December 19, 1845, by the provisional government of Oregon Territory.