| Bill Mountjoy | |
| Position: | Pitcher |
| Bats: | Left |
| Throws: | Right |
| Birth Date: | December 11, 1858 |
| Birth Place: | London, Canada West |
| Death Place: | London, Ontario, Canada |
| Debutleague: | MLB |
| Debutdate: | September 29 |
| Debutyear: | 1883 |
| Debutteam: | Cincinnati Red Stockings |
| Finalleague: | MLB |
| Finaldate: | August 18 |
| Finalyear: | 1885 |
| Finalteam: | Baltimore Orioles |
| Statleague: | MLB |
| Stat1label: | Win–loss record |
| Stat1value: | 31–24 |
| Stat2label: | Strikeouts |
| Stat2value: | 164 |
| Stat3label: | Earned run average |
| Stat3value: | 3.25 |
| Teams: |
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William Henry Mountjoy (a.k.a. Medicine Bill) (December 11, 1858 – May 19, 1894) was a Canadian-born pitcher in Major League Baseball.