Cowlitz County is a
county located in the
U.S. state of
Washington. As of the
2010 census, its population was 102,410. The county seat is
Kelso, and its largest city is
Longview. The county was formed on April 21, 1854. Its name derives from the anglicized version of the
Cowlitz Indian term, Cow-e-liske, meaning either “river of shifting sands” or “capturing the medicine spirit.”