Starting at the corner of Main Street and Chicago Drive, M-121 runs northeasterly out of Zeeland on Chicago Drive roughly parallel to I-196. A CSX railroad line also parallels the road to the northwest. The trunkline is a four-lane divided highway bordered by farms.
M-121 starts at the corner of Main Street and Chicago Drive in Zeeland, heading northeasterly along Chicago Drive parallel to I-196. A CSX railroad line runs alongside this road to the northwest. The mainline is a four-lane divided highway with farms on either side.