M-56 was a state trunkline highway in the southeastern part of the US state of Michigan. It existed from 1919 until 1957. The highway ran north from Monroe, where it connected with US Highway 24 (US 24, Telegraph Road), to Flat Rock where it terminated at an intersection with US 24/US 25. Before a series of truncations in the 1950s, the highway continued along the Huron River to New Boston and Belleville. The trunkline was progressively scaled back to Flat Rock before being decommissioned in 1957.