List of county-designated highways in Michigan
The county-designated highways in Michigan comprise a 1,241.6-mile-long (1,998.2 km) system of primary county roads across the US state of Michigan. Unlike the State Trunkline Highway System, these highways have alphanumeric designations with letters that correspond to one of eight lettered zones in the state.
Source: Wikipedia — List of county-designated highways in Michigan (CC BY-SA 4.0)