U.S. Federal Route 42 is a north-south highway in Madison County. It runs in the central and northern portions of the county. U.S. Rt. 42 passes through the following towns in Madison County. London Gillivan Plain City U.S. Rt. 42 is not multi-plexed in Madison County. U.S. Rt. 42 intersects the following highways in Madison County. Ohio State Route 38, at London. Ohio State Route 56, at London. Ohio State Route 142, at London. U.S. Rt. 40, near Layfayette. Interstate 70, near Layfayette. Ohio State Route 29, near West Jefferson.