Dafoe's ancestry includes German (where two of his great-grandparents were born, as were some of Willem’s other, much more distant, ancestors), English, Irish, Northern Irish, Scottish, Swiss-French, and French. Many of his antecedents also lived in Canada.
Willem Dafoe was born as William James Dafoe on July 22, 1955, in Appleton, Wisconsin, the United States, to Muriel Isabel (Sprissler), a nurse, and William Alfred Dafoe, a surgeon.
He is the second youngest of eight children. He has five sisters and one brother. Willem was the only Dafoe to follow an artistic bent, while the rest of the brood took the well-trod professional route, becoming lawyers, nurses, and doctors.