 M-123 is a state trunkline highway in the eastern Upper Peninsula of the U.S. state of Michigan. It is one of only a few highways in Michigan that curve around and form a U-shape. In fact, M-123 has three intersections with only two state trunklines. It meets M-28 twice as a result of its U-shaped routing. M-123 also has a rare signed concurrency with a County-Designated Highway in Michigan; in Trout Lake, there is a concurrency with H-40. All of M-123 north of M-28 is a Scenic Heritage Route within the Michigan Heritage Route system.
