St Illtyd's church is located in a high-set position on the east side of Penrhiwfer Road at its junction with Ashdale Road. It was built in 1891-4 to designs of architect E.M.Bruce Vaughan of Cardiff.
The first organised Anglican services in connection with the present church were held in Williamstown Board School in 1884. These services grew from the early Welsh services held in the neighbouring village, Penygraig. Eventually, an English service was held on Sunday afternoons, the priest in charge being attached to the adjoining parish of Cymmer. The foundation stone of the new church was laid at Penrhiwfer on August 6th, 1891. The first building erected consisted of nave and bell-tower, and had neared completion for roofing, when the arch and bell-tower fell, the side walls collapsing, injuring three of the faithful members, all of whom sustained serious injury. The collapse was due to the underminning in the area causing subsidence.
The finished church is built in Decorated style and consists of nave and lower, narrower, chancel under slate roofs incorporating a bell tower; south-west gabled porch and north-west double cross gabled vestry of two storeys.
The consecration services was conducted on April 30th 1894, by the Bishop of Llandaff. The cost of the building was £1,580, and would accomadate 310 worshipers.

Sources:
http://www.parishofpenygraig.org/stilltyd.htm
J.Newman, Buildings of Wales: Glamorgan (1995), p.514.

David Leighton, RCAHMW, 16 December 2014