Carmarthen County Hall was designed in 1935 by Sir Percy Thomas but not completed until 1955. The county hall replaced the Carmarthen Gaol built by John Nash on part of the site of Carmarthen Castle. The portico of the Nash gaol was dismantled for re-erection, but the stones were mislaid during the war.

The county council was formed in 1889, operated first from the County Clerk's private office in Llandovery, then from Bank House, Spilman Street from 1907. The gaol site was bought in 1924 and various plans for conversion made before the decision for a new building was taken in 1934. Work stopped in 1942 and resumed in 1946. The council chamber was completed last.

The building is in Chateau style, using rock-faced grey Forest of Dean stone with some Portland stone dressings and steep roofs of grey-green slate. There are four ranges each with massive roof bell-cast at eaves and the 2 long sides ended in full-height curved bays carried up as curved pavilion roofs. There is a broad doorcase in Portland stone carved with 11 relief shields by David Evans illustrative of the county council's operations (education, health, weights and measures, car taxation etc).

Reference: Cadw listed buildings database.