Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. M-31 was a state trunkline highway in the Lower Peninsula in the US state of Michigan. It served as a connecting route between Saginaw, The Thumb communities, and Port Huron.The route of M-31 can still be driven today. With US 31 being commissioned in 1926, the route was renumbered in several segments. M-31 started at the 1920s version of M-21 and followed modern M-25 northward to Harbor Beach. There M-31 would follow today's M-142 westward through Bad Axe and Pigeon back to the modern M-25. Once back on the modern M-25, M-31 passed through Sebewaing southwesterly to the modern M-24 and south to Unionville. Once M-31 met up with the modern M-138 it turned westerly through Akron and Fairgrove to Bradleyville Road. Bradleyville Road connected through Gilford to the current M-81. M-31 followed M-81 west to Saginaw, and the terminus at what was then M-10.