The State Trunkline Highway System was formed on May 13, 1913, and several sections of the system were designated along the course of the then-future I-75. Division 1 connected the Ohio state line northeasterly to Detroit, and Division 2 connected Detroit with Mackinaw City. A branch of Division 7 ran north from St. Ignace to Sault Ste. Marie. The system was signposted in 1919, and those highways were marked on maps for the first time. The first M-10 was designated along the highways from Ohio through Detroit to Standish. M-76 connected Standish with Grayling, where the first M-14 ran northward to Cheboygan. From there, M-10 connected to Mackinaw City. In the UP, M-12 connected St. Ignace with Sault Ste. Marie along a route to the east of the old Mackinac Trail. When the United States Numbered Highway System was formed on November 11, 1926, most of these highways were redesignated as part of the national system. From the state line northward, M-10 was included as a part of US 24 and US 25. At Detroit, M-10 was used as a part of US 10. North of Grayling, M-14 was redesignated as a part of US 27. M-12 was used for US 2.