| Dennis O'Neill | |
| Position: | First baseman |
| Bats: | Unknown |
| Throws: | Left |
| Birth Date: | November 22, 1866 |
| Birth Place: | Holyoke, Massachusetts, U.S. |
| Death Place: | Rushville, Indiana, U.S. |
| Debutleague: | MLB |
| Debutdate: | June 18 |
| Debutyear: | 1893 |
| Debutteam: | St. Louis Browns |
| Finalleague: | MLB |
| Finaldate: | July 26 |
| Finalyear: | 1893 |
| Finalteam: | St. Louis Browns |
| Statleague: | MLB |
| Stat1label: | Batting average |
| Stat1value: | .120 |
| Stat2label: | Home runs |
| Stat2value: | 0 |
| Stat3label: | Runs batted in |
| Stat3value: | 2 |
| Teams: |
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Dennis O'Neill (November 22, 1866 – November 15, 1912) was an American Major League Baseball player. He played for the St. Louis Browns in June, 1893.