| William Ryerson Dempsey | |
| Office1: | Ontario MPP |
| Term Start1: | 1898 |
| Term End1: | 1902 |
| Predecessor1: | John Caven |
| Successor1: | Morley Currie |
| Constituency1: | Prince Edward |
| Party: | Conservative |
| Birth Date: | 2 April 1832 |
| Birth Place: | Prince Edward County, Canada West |
| Death Place: | Prescott, Ontario |
| Occupation: | Farmer |
William Ryerson Dempsey (October 4, 1832 - February 13, 1914)[1] was a farmer and politician in Ontario, Canada. He represented Prince Edward in the Legislative Assembly of Ontario from 1898 to 1902 as a Conservative member.
The son of William Dempsey and Sarah Mikel, he was born in Prince Edward County, Upper Canada and was educated at the normal school in Toronto. Dempsey taught school for several years and then became a fruit grower and fruit dealer. He served as township reeve for six years and was warden for Prince Edward County, also serving as a justice of the peace. Dempsey was a Captain in the 16th Prince Edward Battalion during the Fenian raids. He married Emily Boulter.[2]