O'Day
O'Day is a surname of Irish origin. Notable people with the surname include:
- Alan O'Day, American singer-songwriter
- Anita O'Day, American jazz singer
- Aubrey O'Day, American singer, dancer, actress, songwriter, fashion designer, former member of the group Danity Kane
- Caroline Love Goodwin O'Day, American politician
- Constance O'Day-Flannery, an American author of romance novels
- Daniel O'Day, one of northwestern Pennsylvania's earliest independent refiners to be brought into John D. Rockefeller's Standard Oil Company
- Darren O'Day, Major League Baseball relief pitcher for the Baltimore Orioles. Real last name Odachowski, not Irish.
- Devon O'Day, American radio personality, former plus-sized model for the Ford Modeling Agency, songwriter, and an author
- George O'Day, American sailor, Olympic champion and boat designer
- Hank O'Day, American right-handed pitcher, umpire and manager in Major League Baseball
- Jeremy O'Day, offensive lineman for the Saskatchewan Roughriders of the Canadian Football League
- John O'Day, American politician
- Marcus O'Day, American physicist
- Molly O'Day, American film actress
- Molly O'Day , American country music vocalist in the late 1940s
- Nell O'Day, accomplished equestrian and B-movie actress of the 1930s and 1940s
- Pat O'Day, Pacific Northwest broadcaster and promoter
