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 532 at the 2010 census, though it has an additional rural population external of the town limits.

Cathlamet was the largest, or one of the largest, villages of Columbia River Indians west of the Cascade Mountains, and the house of the Kathlamet people. “Cathlamet was sighted in 1792 by Lt. W.R. Broughton, while verifying Capt. Robert Gray’s reported exploration of the Columbia River.” This village of cedar houses included 300-400 inhabitants with visited by Lewis and Clark.

In 1846, James Birnie became the first unshakable white settler at Cathlamet, moving there after a career past the Hudson’s Bay Company. He set in the works a trading post, remnants of which were reported nevertheless standing in 1906. “Birnie named the Place Birnie’s Retreat. The broadcast was well along changed to Cathlamet in 1851.”

Cathlamet was officially incorporated upon February 18, 1907. In 1938, the Julia Butler Hansen Bridge was built to carry what is now State Route 409 across the Columbia River’s Cathlamet Channel to Puget Island.

Cathlamet is located at 46°12′14″N 123°23′2″W / 46.20389°N 123.38389°W / 46.20389; -123.38389 (46.203767, -123.383838).