M-158 (Michigan highway)

M-99
M-99 highlighted in red
Route information
Maintained by MDOT
Length:	86.058 mi (138.497 km)
Existed:	1940 – present
Major junctions
South end:	SR 15 near Pioneer, OH
	M-34 near Osseo US 12 in Jonesville M-49 in Litchfield M-60 in Homer I-94 near Albion M-50 in Eaton Rapids I-96 in Lansing
North end:	I-496 / Capitol Loop in Lansing
Location
Counties:	Hillsdale, Calhoun, Jackson, Eaton, Ingham
Highway system
Michigan State Trunkline Highway System Interstate US State Byways ← M-98 M-100 → ← M-8 M-9 US 10 → ← M-157 M-158 M-160 →

M-99 is a north–south state trunkline highway in the Lower Peninsula of the US state of Michigan. It runs from the Ohio state border, where it connects to State Route 15 (SR 15), north to Lansing, where it terminates at a junction with Interstate 496 (I-496) and the Capitol Loop. The highway mainly serves local communities along the route as it passes through farm lands in the southern part of the state. One segment is routed concurrently with US Highway 12 (US 12) in Jonesville while the northern end runs through urban areas on a street named for Martin Luther King, Jr. in Lansing.

The current highway is the third to carry the M-99 designation. The others were located near Lake Michigan near Muskegon in the Lower Peninsula and Gulliver in the Upper Peninsula in the 1920s and 1930s. The current highway was first designated as parts of M-34 and M-64 in 1919. These numbers were later dropped in favor of an M-9 designation in 1929. For part of 1934, a loop route was designated M-158 in Hillsdale County that was used for a rerouted M-9 in the area. The M-99 designation was applied to the highway in 1940. Since then, the state has completed paving twice; one segment was returned to gravel surface for two years in the 1950s. The southern section in Hillsdale County was rerouted in the 1960s, and sections were converted into divided highways in the late 1970s.