| William John MacKay | |
| Parliament: | Ontario Provincial |
| Term Start: | September 30, 1929 |
| Term End: | April 3, 1934 |
| Predecessor: | Foster Graham Moffatt |
| Successor: | constituency dissolved |
| Riding: | Bruce South |
| Party: | Liberal |
William John MacKay was a Canadian politician from the Ontario Liberal Party. He represented Bruce South in the Legislative Assembly of Ontario from 1929 to 1934.[1]