| Billy Mahoney | |
| Fullname: | William James Mahoney |
| Birth Date: | 1 January 1885 |
| Birth Place: | Geelong, Victoria |
| Death Place: | Hawthorn, Victoria |
| Originalteam: | Barwon Juniors |
| Height: | 170 cm |
| Weight: | 67 kg |
| Statsend: | 1920 |
| Years1: | 1902 |
| Club1: | Geelong |
| Games Goals1: | 17 (11) |
| Years2: | 1904–1905 |
| Club2: | St Kilda |
| Games Goals2: | 17 (9) |
| Years3: | 1908–11,1913-15,1920 |
| Club3: | Richmond |
| Games Goals3: | 114 (53) |
| Games Goalstotal: | 148 (73) |
William Mahoney (1 January 1885 – 26 November 1939) was an Australian rules footballer who played for the Geelong Football Club in the VFL in 1902 and for the St Kilda Football Club between 1904 and 1905. He then played for the Richmond Football Club in the VFA in 1906 and 1907 then in the VFL on and off between 1908 and 1920.