M-27 is a north–south state trunkline highway in the extreme north of the Lower Peninsula of the US state of Michigan. The trunkline runs between Interstate 75 (I-75) just north of Indian River and Cheboygan, where it meets US Highway 23 (US 23) near Lake Huron. It remains as a relic of the old US 27 which disappeared north of Grayling after being supplanted by I-75, which lies close to old US 27 between Grayling and Indian River.

The State Trunkline Highway System consists of all the state highways in Michigan, including those designated as Interstate, United States Numbered, or State Trunkline highways. In their abbreviated format, these classifications are applied to highway numbers with an I-, US, or M- prefix, respectively. The system is maintained by the Michigan Department of Transportation (MDOT) and comprises 9,669 miles (15,561 km) of trunklines in all 83 counties of the state on both the Upper and Lower peninsulas, which are linked by the Mackinac Bridge. Components of the system range in scale from 10-lane urban freeways with local-express lanes to two-lane rural undivided highways to a non-motorized highway on Mackinac Island where cars are forbidden. The longest highway is nearly 400 miles (640 km) long, while the shortest is about three-quarters of a mile. Some roads are unsigned highways, lacking signage to indicate their maintenance by MDOT; these may be remnants of highways that are still under state control whose designations were decommissioned or roadway segments left over from realignment projects.