U.S. Highway 23 (US 23) is a United States Numbered Highway that runs from Jacksonville, Florida to Mackinaw City, Michigan. In the U.S. state of Florida, US 23 is concurrent with US 1 south of Alma, Georgia, except in Downtown Jacksonville. US 23 is also concurrent with US 301 between Homeland, Georgia and Callahan. In the Jacksonville area, US 23 is the unsigned State Road 139 (SR 139), which also continues east from the south end of US 23 along SR 10A to SR 115 near the Mathews Bridge.