The Steilacoom are an unrecognized Native American tribe located in Washington state in the United States.
Traditionally situated in the area southwest of what is now Tacoma, Washington, the Steilacoom spoke a sub-dialect of the Salish language. The tribe was thought to have numbered about 500 members prior to contact with European settlers, though by 1853 a smallpox epidemic had decreased that number to about twenty-five individuals. In 1854 the remnants of the tribe entered into the Medicine Creek Treaty, but did not receive a permanent reservation.
Beginning in 1929, tribal members embarked on an unsuccessful process of official recognition by the United States government. As of the early 2000s, the tribe claimed about 600 members, however, a 2008 investigation by the Bureau of Indian Affairs (BIA) found that "only three of them are documented descendants of persons described in 19th and early 20th century documents as Steilacoom Indians" with the remainder having Native ancestry from other sources. The Nisqually and Puyallup tribes have opposed the Steilacoom attempts at recognition on those grounds. The BIA has declared the Steilacoom an extinct tribe.