 The 1927 edition of the official Michigan highway service map was the first to show M-28 extended along US 41 into Marquette County and east over the former M-25 through Munising and Newberry, before ending in downtown Sault Ste. Marie. At Negaunee, M-28 was shown along the previous routing of M-15 between Negaunee and Marquette for 10 miles (16 km), while US 41 ran along a portion of M-35. This southern loop routing of M-28 lasted until approximately 1936, when M-28 was displayed as concurrent with US 41. The former route is now Marquette County Road 492 (CR 492). Around 1930, the northern terminus of US 41 was extended east from Copper Harbor to Fort Wilkins State Park. Another realignment shown in 1937 marked the transfer of US 41 / M-28 out of downtown Ishpeming and Negaunee. This former routing later became Bus. M-28. The highway was realigned due north between Rapid River and Trenary according to the 1938 service map. US 41 was completely paved in 1951. The final two sections to be paved were in Baraga County and Keweenaw County.
