Michigan State Route 43 was an east-west highway in across Central Kalamazoo County. Currently, it runs in two sections of Kalamazoo County. The western section runs northwest of the City of Kalamazoo from the Van Buren/Kalamazoo County Line to the Kalamazoo/Allegan County Line. On the eastern section, MI St Rt 43 dips back into the county from Barry County near Richland.
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.
Info on MI St Rt 43 is broken down to the Eastern, Western, and Former Alignments of the highway.