U.S. Route 231 (US 231) in Indiana is a main north–south highway, in the western part of the state. The southern terminus of US 231 is at the Kentucky state line and the northern terminus is at the US 41 just south of St. John. The highway has a mix of expressway and two-lane roadway. The expressway is mainly in southern Indiana and around the Lafayette area, with the rest mainly being two-lanes.

The history of the route is that it was first signed as a state road from Spencer to Lafayette. North of Lafayette the road was a U.S. Highway, until it was decommissioned in favor of US 231. The future of this route, is for it to become an expressway in southern Indiana from the current northern terminus of the expressway to the future interchange at Interstate 69 (I–69). Future for the road around Lafayette will be to bypass Lafayette around the west side of the town.

US 231 has two segments that are included as a part of the National Highway System (NHS). The first is from the Kentucky state line to SR 558 and the second is from I-70 to Lafayette. The NHS is a network of highways that are identified as being most important for the economy, mobility and defense of the nation. The highway is maintained by the Indiana Department of Transportation (INDOT) like all other U.S. Highways in the state. The department tracks the traffic volumes along all state highways as a part of its maintenance responsibilities using a metric called average annual daily traffic (AADT). This measurement is a calculation of the traffic level along a segment of roadway for any average day of the year. In 2010, INDOT figured that lowest traffic levels were the 1,100 vehicles and 180 commercial vehicles used the highway daily from US 52 to I–65. The peak traffic volumes were 27,990 vehicles and 1,950 commercial vehicles AADT along the section of US 231 that is concurrent with US 52.

US 231 enters Indiana on the William H. Natcher Bridge over the Ohio River from Kentucky. The road enters as a four-lane divided highway and immediately has a folded diamond interchange with State Road 66 (SR 66). The highway heads north passing by a power plant and through farmland on the way towards Dale. The expressway has an intersection with SR 70. The route turns northeast passing through woods, just south of the Lincoln State Park. The road turns due north having an interchange with SR 162, this exit is access to the State Park. The expressway turns northwest and enters Dale. On the south side of Dale is an intersection with SR 62, this is the old route of US 231. The highway turns northeast again, around the northwest side of Dale. The route has an interchange with I–64. At the Dubois County line, the highway enters Eastern Time Zone. Also at the Dubios County line, the expressway ends and US 231 becomes a two-lane rural highway.

The road heads north-northeast towards Huntingburg, passing through rural farmland. The highway enters Huntingburg from the south passing through residential areas of town. The route has a traffic light in downtown Huntingburg with SR 64. North of downtown Huntingburg the road passes through commercial properties, before leaving town. The highway heads north towards Jasper, on the ways passing by a mix of both farmland and woodland. The road enters Jasper from the south passing by commercial lots. West of downtown the route begins a concurrency with SR 56, with both routes heading east. The concurrency enters downtown and has a traffic light at the northern terminus of SR 64. That is intersection US 231 and SR 56 turn towards the north. The two highways head north out of downtown and into residential areas. The road leaves Jasper heading northeastward toward Loogootee. In Haysville, the concurrency with SR 56 ends. US 231 heads due north-northeast from SR 54, before turning more northward. The highway enters Loogootee and begins a concurrency with both U.S. Route 50 (US 50) and US 150. The concurrency heads due north, then turning northeast and entering downtown Loogootee. In downtown the concurrency ends, with US 50 and US 150 heading east and US 231 heading northwest. The road heads north towards Bloomfield, passing the Naval Surface Warfare Center Crane Division.

The route enters Bloomfield form the south beginning a concurrency with SR 54 in downtown. This intersection is also the southern terminus of SR 157. US 231 and SR 54 head due west after about 4 miles (6.4 km) the concurrency wnd with SR 54 keeps heading due west and US 231 turning due north. This intersection is the northern terminus of SR 57. US 231 heads north for about 4 miles (6.4 km), until SR 67. The two routes head northeast heading towards Spencer, along the banks of the White River. The highway turns towards the north away from the river and the concurrency ends. SR 67 heads northeast again and US 231 heads northwest. The road heads towards Cloverdale, passing through an intersection with SR 42. The route enters Cloverdale passing by a mix of commercial and residential properties. On the north side of Cloverdale the highway becomes a four-lane divided highway, with an interchange at I–70.

North of I–70, the road narrows to a two-lane highway still heading towards the northwest. The route has a traffic light at US 40 south of Greencastle. The highway enters Greencastle from the southeast and begins to turn due north. In downtown Greencastle the highway has a traffic light with the western terminus of SR 240. US 231 leaves Greencastle heading due north for Crawfordsville, passing through a traffice light at US 36. On the south side of Crawfordsville the route becomes a four-lane undivided highway, passing through commercial use properties. The road heads towards downtown Crawfordsville, and begins a concurrency with both SR 32 and SR 47. The concurrency passes the Wabash College and an intersection with US 136. At this intersection the concurrency with both SR 32 and SR 47 turns east onto US 136. US 231 becomes a four-lane divided highway north of US 136, becoming an undivided highway again, heading through the north side of Crawfordsville. Through the north side of Crawfordsville the road passes through a mainly residential land, with a few commercial lands near the interchange with I–74.

North of I–74, the road returns to a two-lane rural highway and heads due north for Lafayette. On the way to Lafayette the route passes through rural farmland, paralleling a CSX rail line. The road enters Lafayette and becomes a four-lane divided highway with a mix of both residential and farmland. The highway has a traffic light at SR 25. The route now crosses the Wabash River and heads for West Lafayette. The highway has an interchange at SR 43 and Old US 231. From this interchange the road heads west on parallel one-way streets, with northbound on Fowler Avenue and southbound on Wiggins Street. The two directions come back together and form a four-lane undivided highway, forming the northeast boundary of Purdue University. After Purdue, the highway begins a concurrency with US 52. The concurrency starts as a four-lane divided highway becoming a four-lane undivided highway. The two routes turn northwest bound and US 231 leaves the concurrency, with US 52 continues northwest bound and US 231 heads due north.

North of US 52 the highway is a two-lane rural highway, passing through farmland. The road has an interchange with I–65, this is the first of four interchanges with I–65. The route begins a concurrency with US 24 in Wolcott. The two highways head north through Wolcott and then turn due west. After Wolcott, the concurrency crosses into Jasper County and also into Central Time Zone. The two routes have an interchange at I–65 east of Remington. In Remington the two highways end the concurrency, with US 24 continues due west and US 231 heads due north again. The road now enters Rensselaer, heading north turning northeast and has a traffic light at SR 114. North of the traffic light the road makes a sharp turn and heads northwest. North of Rensselaer, the route turns due north, heading towards SR 10. At SR 10, US 231 turns due west concurrent with the state road. After 2.5 miles (4.0 km) the concurrency ends, with SR 10 heading due south and US 231 heading due north. The highway enters Porter County on a bridge over the Kankakee River.

North of the Kankakee River the route begins a concurrency with SR 2 at a four-way stop south of Hebron. The concurrency enters Hebron from the south passing mainly residential areas. The concurrency has an intersection with the western terminus of SR 8 at the main intersection in downtown. North of downtown the concurrency with SR 2 ends with SR 2 heading due north and US 231 heading northwest. The road leaves Hebron passing more residential properties, heading towards Crown Point. On the southeast side of Crown Point the route has its last interchange with I–65. After I–65 the road has an intersection with ST 55. Passing through the southeast side of Crown Point the road is lined with housing additions on either side. The road begins a concurrency with SR 55 and the two roads head for downtown Crown Point. In downtown Crown Point the roads go around the county court house, on one-way streets. The concuurency ends when the state road heads due north. US 231 leaves Crown Point, heading towards its northern terminus on the south side of St. John. The route turns due west for the last few miles and to meet US 41. US 231 meets US 41 at an intersection controlled by a traffic light.

Between 1918 and 1926, US 231 was signed SR 18 from Rockport to Old SR 4 and then followed Old SR 4 to Jasper. From Jasper to Bloomfield the route was unimproved county roads. Bloomfield to Switz City the future US 231 would follow Old SR 30. North of Switz City the road was SR 12 this road is now SR 67. From Jasper to Lafayette the road was number as SR 32, where future US 231 followed SR 29, this is now US 52. The roadway from SR 29 until Wolcott was given SR 45 has a number. Wolcott to Remington the route followed SR 7. North of Remington the road was number SR 8 north to Hebron. From Hebron to the current terminus was an unimproved county road. This system was change on 1926 when the U.S. Highways were created.

The current number system in Indiana was put into place in 1926. The route that would become US 231 was signed as SR 45 from Rockport to SR 58 in Scotland. From Scotland to Bloomfield it was an unimproved county road. From Bloomfield to Spencer US 231 was given the same number that the route is concurrent with today. North of Spencer to Lafayette was number SR 43. The route that US 231 followers today along US 52 was the same. Then SR 53 from US 52 to Crown Point and SR 8 from Crown Point to US 41. The section of US 231 north of US 52 to US 41 was signed as US 152. The US 152 was used between 1934 and 1938, in 1938 US 152 was decommissioned. The road went back to state road numbers, this lasted until 1952 when US 231 was commissioned and signs installed.

US 231 was first signed in Indiana in 1954 and the whole length of US 231 was two-lanes. In Southern Indiana the road has been winded from two-lanes surface road to a four-lane divided expressway. The expressway construction began in 2002 with a new bridge over the Ohio River and the state designated the old bridge near Owensboro, KY as SR 161. When the bridge was completed traffic had to exit the expressway at the first exit, SR 66. The expressway was build north towards Dale, on all new terrain, with some of the old highway being signed as SR 161, SR 62 and the rest becoming county roads. US 231 was moved onto the expressway in March 15, 2011.

The future of US 231 has two different projects with the first in southern Indiana and the second in Lafayette. Both projects will make US 231 a four-lane divided highway.

This project will build a bypass of Huntingburg and Jasper.

This project is a western bypass of Lafayette this route will be concurrent with US 52. The bypass will be a four-lane divided highway.