| William Rees Brock | |
| Constituency Mp: | Toronto Centre |
| Parliament: | Canadian |
| Predecessor: | George Hope Bertram |
| Successor: | Edward Frederick Clarke |
| Term Start: | 1900 |
| Term End: | 1904 |
| Birth Date: | 14 February 1836 |
| Birth Place: | Eramosa Township, Upper Canada |
| Party: | Conservative |
William Rees Brock (February 14, 1836 - November 1, 1917) was a Canadian businessman and politician.
Born in Eramosa Township, Upper Canada, Brock was president of W. R. Brock Co., Limited which sold wholesale dry goods, woolens, and carpets. He was elected to the House of Commons of Canada in the 1900 federal election for the electoral district of Toronto Centre. A Conservative, he did not run in 1904.