The Suzzallo Library at the University of Washington has the best collection of biographical materials for Washington residents. The Family History Library has some compiled biographies of explorers, Indians, prominent citizens, and early settlers in the state. There is no statewide index to biographies.
Biographical information is often found in state and local histories. Another helpful biographical source is Who's Who in Washington State: A Compilation of Biographical Sketches of Men and Women Prominent in the Affairs of Washington State (Seattle, Washington: H. Allen Pub., 1927; FHL film 1000645 item 5).