In 1931, the state transferred US 31 to a new routing between the St. Joseph and South Haven areas; in the process, the former route of US 31 between Watervliet and South Haven was redesignated as M-140. The highway was extended southward from Watervliet to the Niles area in late 1934 due to heavy traffic on that section. The concurrency between M-62 and M-140 was eliminated around the end of 1957 when the former highway was truncated to terminate east of Eau Claire instead of continuing west into town. In 1958, the route north of Watervliet to the county line was realigned, smoothing several sharp curves.