| John T. Alsop | |
| Office1: | 33rd & 35th Mayor of Jacksonville |
| Term Start1: | 1941 |
| Term End1: | 1945 |
| Predecessor1: | George C. Blume |
| Successor1: | C. Frank Whitehead |
| Term Start2: | 1923 |
| Term End2: | 1937 |
| Predecessor2: | John W. Martin |
| Successor2: | George C. Blume |
| Birth Date: | 10 August 1874 |
| Birth Place: | Enfield, North Carolina, U.S. |
| Death Place: | Jacksonville, Florida, U.S. |
| Party: | Democrat |
John Thomas Alsop Jr. (August 10, 1874 – May 12, 1958) was an American politician. He served as Mayor of Jacksonville, Florida, from 1923 to 1937, and again from 1941 to 1945. His eighteen-year, seven term stint in the mayor's office is the longest in the city's history. Jacksonville's Main Street Bridge, officially the John T. Alsop Jr. Bridge, is named for him.