William Macomb (c. 1751 – April 16, 1796) was a British colonial merchant and fur trader in the Detroit, Michigan area before and after the American Revolutionary War. He got his start as a young man in the colony of New York. He was a brother of Alexander Macomb, and the two were partners in Detroit.
After the war, Macomb was elected as a member of the first parliament of Upper Canada in 1792, and he was the largest slaveholder in the area of Michigan at the time of his death. He died shortly before the British evacuated from Fort Detroit under the Jay Treaty, which was ratified in 1795.