Trefenty was the ancient caput of the lordship of Oysterlow (Ystlwyf), which lay mainly between the rivers Cynin and Cywin, and was roughly coterminous with the parish of Llanfihangel Abercowin (whose parish church, St Michael's (NPRN 102138) was situated some 360m south-east of Trefenty farm). The farm is located some 150m east-north-east of a motte and bailey castle, Castell Aber Taf (NPRN 304187), which may have preceded the house itself. Ystlwyf was owned by the Anglo-Norman lords of St Clears until 1171 when it was acquired by Rhys ap Gruffydd. He granted the area to the Cistercian Abbey at Whitland in 1214, as part of the Osterlow Grange. After the dissolution, Sir John Perrot acquired the grange. He therefore owned Trefenty in the late sixteenth century, when his daughter and heiress resided here with her husband, Sir William Lower (died 1615), a noted scholar and astronomer. William was succeeded by his son, Thomas (died 1661) and then his daughter, Dorothy. Her daughter married Edmond Plowden, Plowden Hall, salop, after which Trefenty was tenanted. A later tenant, John Waters, was the last person to be buried at the adjacent St Michael's Church (NPRN 102138). The Plowdens sold Trefenty to the Ecclesiastical Commissioners in the 1870s. Ownership passed to the University of Wales in 1920. It is now a working farm.

The house is a Grade II listed building, whose structure is late eighteenth- early nineteenth century in character. However, its steep roofs and double-pile plan are thought to possibly indicate progressive remodelling around an older core. The building consists of two parallel three-window ranges, with painted timber sash windows, bracketed eaves and slated roofs. The east facade has six-pane sash windows to the attic, the rest being twelve-pane. The right bay has its original timber door.The gutters and downpipe are cast-iron. The door is partially obscured by a projecting single-storey extension, thought to date to the twentieth century. This has a tall red brick chimney stack. The west facade resembles the east. It has a central gabled porch, with a small window in its west gable and a door in its north side. The south facade has two plain, matching gables separated by a narrow channel, in which lies a pitched slated roof, terminating above a twelve-pane sash window between the gables. the north facade has two similar gables, but these are joined at attic level. according to local tradition, there was once a roofed passage in front of Trefenty, along which funerals, weddings and the normal congregation had a right to pass on their way to the church. No physical trace of this remains.

Trefenty house is said to be where the saying 'Golch Trefenty' ('Trefenty wash') originated. Historically the household at Trefenty was large, as was the amount of washing to be seen on washing day. Therefore when a housewife had an unusually large wash load, she was said to have a 'Golch Trefenty'.

Sources include:
Cadw, Listed Buildings Database
www.cambria.org.uk/HLC/EstuaryArea/area155.htm

N Vousden, RCAHMW, 7 November 2012