The Kathlamet people are a tribe of Native American people with a historic homeland along the Columbia River in what is today southwestern Washington state. The Kathlamet people originally spoke the Kathlamet language, a dialect of the Chinookan language. They were also called "Guasámas, or Guithlamethl, by the Clackamas", and "Kwillu'chini, by the Chinook."
The state of Washington was the historic homeland of the Kwillu'chini people.