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 Canadian House of Commons 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:
On 22 September 1921, he was appointed to the Canadian Senate on the recommendation of Arthur Meighen. He represented the senatorial division of Grenville, Ontario until his death.