John Dowsley Reid, PC (1 January 1859 – 26 August 1929) was a Canadian businessman, physician, and parliamentarian. A Conservative, he was a long-standing Member of Parliament in the House of Commons of Canada for the Ontario Electoral district of Grenville South (named simply Grenville after 1903). He was first elected in the Canadian federal election of 1891 and was re-elected seven more times. During his years in the House of Commons, he served as a cabinet minister in a variety of posts in the Cabinet of Canada, including: