William Day

William, Will, Bill, or Billy Day may refer to:

• William Day (lithographer) (1797–1845), British lithographer and watercolour artist
• Bill Day (filmmaker) (born 1959), American documentary filmmaker
• Bill Day (cartoonist), American cartoonist

• William Day (Australian politician) (fl. 1861), Australian politician in New South Wales
• William R. Day (1849–1923), American diplomat and Supreme Court Justice
• William Louis Day (1876–1936), American judge
• William J. Day (1876–1950), American judge from Massachusetts
• William S. Day (1923–1984), American politician in the state of Washington

• William Day (horseman) (1823–1908), British racehorse trainer
• Bill Day (baseball) (1867–1923), American baseball player
• Bill Day (alpine skier) (1934–2024), Australian Olympic skier
• Billy Day (1936–2018), English footballer
• Will Day (born 2001), Australian rules footballer

• William Day (bishop) (1529–1596), English clergyman
• William Day (divine) (died 1684), English clergyman
• William Day (sea captain) (1715–1797), American naval captain
• William Day (architect) (fl. 1800), Irish architect
• William H. Day (1825–1900), American abolitionist