William Gillis may refer to:
- Willie Gillis, Norman Rockwell's fictional character
- Willie Gillis, a television character in The Rookies
- Bill Gillis (1936–2009), Canadian politician
- William Gillis (businessman) (1788–1869), American businessman and one of the 14 original founders of Kansas City, Missouri
- William Gillis (politician) (1859–1929), British Member of Parliament for Penistone