William Day may refer to: William H. Day (1825–1900), U.S. Black abolitionist William Day (bishop) (1529–1596), English clergyman William Day (divine) (died 1684), English clergyman William Day (sea captain) (1715–1797), Massachusetts naval captain during the American Revolutionary War William Day (architect), Irish architect from County Wexford William Day (horseman) (1823–1908), British racehorse trainer William Day (lithographer) (1797–1845), British lithographer and watercolour artist William Day (Australian politician) (fl. 1861), member of the New South Wales Legislative Council William J. Day (1876–1950), judge from Masschusetts William Louis Day (1876–1936), American judge William Peyton Day (1886–1966), architect and co-founder of architectural firm Weeks and Day with Charles Peter Weeks William R. Day (1849–1923), American diplomat and Supreme Court Justice William S. Day (1923–1984), American politician in the state of Washington Will Day, former chair of the UK Sustainable Development Commission Bill Day (cartoonist), American cartoonist Bill Day (baseball) (1867–1923), Major League Baseball player Bill Day (politician), Virginia Bill Day (alpine skier) (born 1934), skied for Australia at the 1952 Winter Olympics Bill Day (filmmaker), American documentary filmmaker