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.