M-115 is a state trunkline highway in the northwestern part of the Lower Peninsula of the US state of Michigan. The highway takes a generally southeast-to-northwest direction between Frankfort on Lake Michigan and Clare in the central part of the state. The northwestern end is at M-22 next to Betsie Lake; the southeastern end in downtown Clare is at an intersection with Business US Highway 127 (Bus. US 127) and Bus. US 10. In between, the trunkline runs about 96+1⁄2 miles (155.3 km) through woodlands, including areas that are a part of either the Manistee National Forest or the Pere Marquette State Forest. The highway also passes agricultural areas, several lakes in the region and a state park near Cadillac.