Following a 1-mile (1.6 km) long concurrency with State Route 235 into McComb, State Route 186 arrives at its northern terminus at its junction with State Route 613.

State Route 186 travels entirely within the northwestern quadrant of Hancock County.

It is not included within the National Highway System.

[3][4] In 1937, State Route 186 was extended north along the current alignment of State Route 235 from Hoytville to that highway's current northern terminus at State Route 65 along the Maumee River northeast of Grand Rapids.

[7][8] The entire route is in Hancock County.