| William McCarthy | |
| Position: | Pitcher |
| Bats: | Right |
| Throws: | Right |
| Birth Date: | 11 April 1882 |
| Birth Place: | Ashland, Massachusetts, U.S. |
| Death Place: | Boston, Massachusetts, U.S. |
| Debutleague: | MLB |
| Debutdate: | April 21 |
| Debutyear: | 1906 |
| Debutteam: | Boston Beaneaters |
| Finalleague: | MLB |
| Finaldate: | April 21 |
| Finalyear: | 1906 |
| Finalteam: | Boston Beaneaters |
| Statleague: | MLB |
| Stat1label: | Win–loss record |
| Stat1value: | 0–0 |
| Stat2label: | Earned run average |
| Stat2value: | 9.00 |
| Stat3label: | Strikeouts |
| Stat3value: | 0 |
| Teams: | |
William Thomas McCarthy (April 11, 1882 – May 29, 1939) was an American professional baseball pitcher. He appeared in one major-league game, pitching two innings in one game for the 1906 Boston Beaneaters. In that game, he gave up two earned runs on two hits and three walks.