William Day
William, Will, Bill, or Billy Day may refer to:
Arts and entertainment
- William Day , British lithographer and watercolour artist
- Bill Day , American documentary filmmaker
- Bill Day, American cartoonist
Law and politics
- William Day , Australian politician in New South Wales
- William R. Day, American diplomat and Supreme Court Justice
- William Louis Day, American judge
- William J. Day, American judge from Massachusetts
- William S. Day, American politician in the state of Washington
Sports
- William Day , British racehorse trainer
- Bill Day , American baseball player
- Bill Day , Australian Olympic skier
- Billy Day, English footballer
- Will Day, Australian rules footballer
Others
- William Day , English clergyman
- William Day , English clergyman
- William Day , American naval captain
- William Day , Irish architect
- William H. Day, American abolitionist