The highway turns westward along Wirtz Road and past the southern terminus of county road F-97 in the northern part of Gladwin County. Near a crossing with the Cedar River, M-18 turns north along Bard Road and then west again along Renas Road. The highway returns to its northerly course when it turns to run along Clarwin Road, which runs along the Clare–Gladwin county line. The roadway angles to the northwest briefly, cutting across the extreme northeast corner of Clare County as the highway crosses into Roscommon County. Through the southern portion of the county, the road runs through the Roscommon forest management unit of the Au Sable State Forest as it approaches Prudenville. In that community, M-18 turns northeasterly and runs along M-55 along the eastern shore of Houghton Lake. The two highways separate on the eastern edge of town, and M-18 turns northward, intersecting the northern end of M-157. M-18 continues north, parallel to Interstate 75 (I-75) near Higgins Lake; M-18 crosses I-75 at exit 239 south of Roscommon. The main entrance to Backus Creek State Game Area is located along this stretch of M-18 just south of I-75.