An unnumbered section of gravel highway was opened in 1937 west of Cadillac; the roadway extended south from M-55 to the Wexford–Lake county line. Later, in 1940, the MSHD renumbered the north–south leg of M-42 from Mesick north to Traverse City and Old Mission. As a result, M-37 was then a discontinuous highway with a gap between M-63 in Peacock to M-115 at Mesick. The spur in Wexford County is shown after 1941 as an "earthen" highway, before disappearing from state maps completely in 1945. A section of M-37 through Newaygo County was renamed in 1945 for Stevens T. Mason, the first governor of the State of Michigan. At the time, Consumers Power Company recommended that all north–south roads in the county bear the name of a state governor as part of a plan to rename the major roads in the county. The company wanted to simplify directions for their employees looking for customers' homes in the area. In the middle of 1948, M-37 was extended to M-55 on a gravel highway that followed the previously unnumbered highway in Wexford County and a new roadway in Lake County. As a result, M-37 still had a gap, but only between M-55 and M-115.