Michigan State Highway 40, or M-40, is a north-south state highway in southwestern lower Michigan. The northern terminus is at U.S. Highway 31 to the south of Holland and the southern terminus on U.S. Highway 12 (the old U.S. Highway 112) near Mottville . It does not quite reach the Indiana state line.
Heading southeastward from Holland, M-40 has an interchange with Interstate 196, it passes through the unincorporated town of Hamilton, then merges with M-89 about six miles northwest of Allegan. In Allegan, it turns south and separates from M-89, passing through Gobles, crossing the Kal-Haven Trail, and forms a junction four miles south with M-43. The junction is known locally as Armstrong Corners. At Paw Paw it intersects with Interstate 94.
Following that it passes through Lawton, Marcellus and then intersects with M-216 . It goes through Jones at the junction with M-60. Its terminus is at U.S. 12.
All of M-40 is an undivided surface route. Between Holland and Allegan it is heavily traveled (M-89 leads to Battle Creek and a junction with US 131, which connects with Kalamazoo).
