| John B. Day | |
|---|---|
 Day in 1884 | |
| Owner / Manager | |
| Born: September 23, 1847 Colchester, Connecticut, U.S. | |
| Died: January 25, 1925 (aged 77) Cliffside, New Jersey, U.S. | |
| MLB statistics | |
| Games managed | 66 |
| Managerial record | 29–35 |
| Winning % | .453 |
| Teams | |
| As manager | |
John Bailey Day (September 23, 1847 – January 25, 1925) was an American tobacco merchant who became an owner and manager in professional baseball of the late 19th century. He was the first owner of the franchise now known as the San Francisco Giants.