The parish of Undal was established as a municipality January 1, 1838 (see formannskapsdistrikt). The municipality existed until 1845, when it was split to form the new municipalities Nord-Undal and Sør-Undal. Prior to the split Undal had a population of 4.695.
Around 1900 the name Undal was Norwegianized to Audnedal.