Michigan State Route 43 runs east-west then north-south in Northwestern Kalamazoo County. It runs from the Kalamazoo/Van Buren County Line, near the Wolf Lake State Fish Hatchery to the Kalamazoo/Allegan County Line, south of Plainwell.
In January, 2019, the City of Kalamazoo and the Michigan Department of Transportation reached an agreement to turn jurisdiction of several streets with in Kalamazoo to be turned over to the city jurisdiction from the states. This eliminated BUSN Loop I-94. BUSN U.S. Rt. 131, and Michigan State Route 43 were eliminated within the city. BUSN U.S. Rt. 131 now runs as a short spur on the north of the city. Michigan State Route 43 was rerouted along U.S. Rt. 131 to Michigan State Route 89. BUSN Spur I-94 and Michigan State Route 343 were created to take the numbering of the highways the state retained where the other highways were removed. MI St Rt 43 passes through the following town in Western Kalamazoo County. Kalamazoo
MI St Rt 43 is multi-plexed in Western Kalamazoo County. U.S. Rt. 131, near Kalamazoo.