Michigan Highway 121 is an old piece of Michigan Highway 21 running between Grand Rapids and Holland. It doesn't quite reach Grand Rapids or Holland, as it's limited to only reaching the next town short of those two destinations. The southwestern end is in Zeeland, the next town east of Holland, at the Interstate 196 business loop. The northeastern end is at exit 69 from Interstate 196's proper freeway in Grandville, the next town west from Grand Rapids. "Chicago Drive" is the name assigned to the road carrying Michigan Highway 121, and it references the fact that this road is part of an old road connecting Grand Rapids to the Chicago area. Interstate 196, which lies just barely to the southeast of Michigan Highway 121, is the modern highway replacing that old route.
My photo of Michigan Highway 121 shows a westbound reassurance marker very near its eastern end at Interstate 196. As Michigan Highway 121 gets its westbound start in Grandville, it goes through a traffic signal right alongside the interchange with Interstate 196. The first westbound reassurance marker for Michigan Highway 121, pictured here, lies just to the west of the traffic signal. This photo was taken along a drive back from Traverse City in March 2018.