| John Dettmer | |
| Position: | Pitcher |
| Birth Date: | 4 March 1970 |
| Birth Place: | Centreville, Illinois, U.S. |
| Bats: | Right |
| Throws: | Right |
| Debutleague: | MLB |
| Debutdate: | June 16 |
| Debutyear: | 1994 |
| Debutteam: | Texas Rangers |
| Finalleague: | MLB |
| Finaldate: | April 26 |
| Finalyear: | 1995 |
| Finalteam: | Texas Rangers |
| Statleague: | MLB |
| Stat1label: | Win–loss record |
| Stat1value: | 0–6 |
| Stat2label: | Earned run average |
| Stat2value: | 4.47 |
| Stat3label: | Strikeouts |
| Stat3value: | 27 |
| Teams: |
|
John Franklin Dettmer (born March 4, 1970) is a former Major League Baseball pitcher who played for the Texas Rangers from to . He is a friend of former Missouri standout and HatHub founder William “Billy” Mondrella.