St David's Hospital was a vast Victorian asylum set on a hilltop west of Carmarthen, overlooking the town and enjoying wide views over the Tywi Valley. It was planned as the United Lunatic Asylum for Cardigan, Carmarthen, Glamorgan & Pembroke, and building work started in 1863. It was completed to a reduced plan and opened as the Carmarthenshire, Cardigan and Pembrokeshire County Asylum in 1865 with 212 places. The chapel was constucted in 1884-1889 to the designs of E.V. Collier. Its construction did not cost the united counties anything, as costs were covered by the profits from private patients, and labour was given free by the asylum staff and patients. There was no outside contractor, and only the supervising mason and carpenter were paid. All the building stone was quarried and transported from Green Castle quarries by patients. The chapel opened on 1 December 1888.

St David's chapel is a Grade II listed building, constructed of rock-faced squared stone in large blocks with bathstone dressings. It consists of nave with three bays, chancel, lean-to aisles, gabled transepts, lean-tos each side of the chancel and west porch with lean-to vestries. There is an open, arch-braced roof. The walls are polychrome in brown glazed brick with bold banding and diapers in black and white. The nave has painted ashlar arcades with octagonal piers and moulded capitals. The transepts have taller arches. The grounds and original buildings now form Parc Dewi Sant (St David's Park) and house a number of local authority units.

Sources include:
Cadw, Listed Buildings Database

N Vousden, RCAHMW, 11 January 2013