US Highway 231 was one of the original United States federal highways commissioned by the American Association of State Highway Officials (AASHO, now AASHTO) in November, 1926. Its original routing, as laid out in the Joint Board on Interstate Highways plan of 1925, was from Montgomery, Alabama to Marianna, Florida. The highway was given the number "231" since it was to be the second branch of US Highway 31 (US Highway 131 was already in existence in Michigan). US 231's total mileage at this point was just over 160 miles.
In 1935, US 231's route in Florida was shifted away from Marianna, and its southern terminus extended to Panama City, where it has since remained. This was the situation until 1954, when US 231 underwent a major northern extension. Heading north from Montgomery, the 231 signs replaced Alabama state highway 11, most of the routing of the now-defunct US Highway 241 in Tennessee; Kentucky state highway 71 through Bowling Green and Owensboro; Indiana state highways 43 and 45, and all of the route of the now-defunct US Highway 152. US 231’s total length was now over 900 miles. Its northern terminus now stands at the junction with US Highway 41 at St. John, Indiana (just south of the Gary, Indiana/Chicago area). In Alabama and Tennessee, it is duplexed with US Highway 431 for some 27 miles.
Today, US 231 remains a major north-south highway except in western Kentucky, where the William H. Natcher Parkway (formerly known as the Green River Parkway) carries its traffic between Owensboro and Bowling Green. It has undergone minor routing changes, again in Kentucky with a new bridge at Owensboro, where US 231 intersects a major east-west route, US Highway 60. From Montgomery, it is the preferred route to the Florida panhandle, and has been upgraded to four-lane expressway status. There is a possibility that US 231 in that area may be upgraded further, to Interstate highway status and carry a proposed number of Interstate 110.
Federal Highway Administration, "US 231 - Indiana to Florida," Highway History
. <http://www.fhwa.dot.gov/infrastructure/us231.htm>. January 2004.
AUTHOR’S NOTE: My family and I have a sort of personal connection with this road. It passes within 100 miles of where I currently live, through Owensboro, Kentucky (where my sister lives), Morgantown, Kentucky (my home town), and ends at Panama City, Florida (where my father lives). I have traveled the entire length of US 231, and its route through Tennessee provides the driver with some of the best scenery the South has to offer. I highly recommend the drive.