It crosses the state mainly in the west-central region, traversing Allen, Warren, Butler, Ohio, and Daviess Counties.

[2] US 231 reaches Butler County to cross I-165 for a second time, and runs concurrently with KY 79 on the southern end of Morgantown.

Both state routes separate from US 231 in the Aberdeen area before crossing the I-165 for a third time before entering Ohio County.

In 2002, US 231 in Daviess County was rerouted from downtown Owensboro onto the then-new William H. Natcher Bridge north of Maceo.

[10][11] The stretch of US 231 from the Natcher Parkway (now I-165) interchange to Bell Street in Morgantown was widened to include a center lane for left-turning in 2013–2014.