Starting in 1918, the Wisconsin Highway Commission erected highway numbers along state-maintained roadways. The highway across the state from St. Croix Falls to Armstrong Creek was numbered WIS 14 at that time. The remainder of what is now US 8 was unnumbered secondary highways, and WIS 14 continued north of Armstrong Creek to Florence. When Michigan numbered its highway system the following year, the future US 8 was not included in the system. In Minnesota, US 8 would follow what was Constitutional Route 46, which was designated in a state constitutional amendment adopted on November 2, 1920; that roadway originally ran between Forest Lake and Chisago City through Wyoming.