Wahkiakum County is a county located in the U.S. state of Washington. As of the 2020 census, the population was 4,422, making it one of the least populous counties in Washington. The county seat and only incorporated town is Cathlamet. The county was formed out of Cowlitz County in April 1854 and is named for Chief Wahkiakum of the Chinook, who is buried in the Pioneer Cemetery in Cathlamet.

Cathlamet is a town located along the Ocean Beach Highway in Wahkiakum County, Washington, United States, where it is the county seat. The population was 560 at the 2020 census.