William Fitzsimmons may refer to:
William Fitzsimmons (Canadian politician) (1818–1894) William Fitzsimmons (Northern Ireland politician) (1909–1992), in Northern Ireland William Fitzsimmons (musician) (born 1978), American singer-songwriter
See also William FitzSimons (1870–1926), Irish-born Australian politician William T. Fitzsimons (1889–1917), a U.S. Army officer