MERTHYR, a parish, in the lower division of the hundred of ELVET, union of CARMARTHEN and county of CARMARTHEN, SOUTH WALES, 4 miles (W.) from Carmarthen; containing 295 inhabitants. This parish is situated in the south-western portion of the county, and is intersected on the west by the river Cywin, which falls into the Tlif at Llanvihangel-Abercowin; and on the south by the turnpike-road leading from Carmarthen to St. Clear's. The living is a discharged rectory, rated in the king's books at £4. 17. 1., and in the patronage of the Crown: the tithes have been commuted for a rent-charge of £165; and there is a glebe of 38 acres, valued at £36 per annum. The church, dedicated to St. Martin, is a small plain building, undistinguished by any architectural details. There are places of worship for Presbyterians, and a class of dissenters who assume no particular denomination; and a schoolroom has been built for the instruction of the poor. Some remains of an ancient monument, thought to be of Druidical origin, are discernible; and within the parish is a farm, once the residence or property of George Vaughan, a Welsh ,judge, called Dedlys, which is supposed to have given its name to that hundred.