William Joseph "Dummy" Deegan (November 16, 1874 – May 17, 1957) was an American professional baseball pitcher. In 1901, he played in two games for the New York Giants of Major League Baseball.
Deegan, nicknamed "Dummy" for being a deaf-mute, was one of three pitchers on the Giants staff in 1901 with that nickname; the other two being Dummy Leitner and Dummy Taylor.