St Illtyd's church is thought to have originated in the twelfth century or earlier. It is neighbours with Cymer Abbey (NPRN 95420), established by the Cistercialn order in 1198. After the dissolution the immediate lands of Cymer were integrated into the parish of Llanelltyd. The church is situated within a curvilinear churchyard, which has been encroached to the south by Ty?n Llan (NPRN 411983). A 1m high raised bank to the immediate west of the church may be natural or may represent a line of earlier raised burials. The churchyard was extended to the west in 1881. Its main entrance is on the north side, and there is a blocked entrance on the north-west side. A secondary entrance in the south-east boundary provides access to Ty?n Llan. An inscribed stone, possibly twelfth century in date, has been set against the interior west wall of the church. It has been interpreted to read 'The footprint of Denyric is affixed on the top of the stone and he himself is bound [by his vow made] before he set out on his journey'. On the end of the stone is the cut outline of a human foot. The stone was found in an outbuilding near the church in 1876.

The church is a Grade II* listed building, with its churchyard walls and gate piers included in the listing. It is constructed of local rubble stone, although some of the lower courses and quoins are made of large cyclopean blocks. The building consists of a continuous nave and chancel with north and south porches. A medieval (possibly twelfth century), cylindrical stoop or font lies loose in the south porch. The lower walls are constructed of large blocks, and are thought to be fifteenth century or earlier. The roof, constructed of six arch-braced collar-beam trusses, is later fifteenth century. The south door, with its four-centred arch, is late medieval in date. The oak door, with chevron decorated hinges, is thought to be fifteenth century in date. The north doorway is of similar design, but probably dates from 1779, the date inscribed upon it. The building was probably restored in 1686 (the date of a date stone to the east of the north porch). Two gabled dormer windows above the windows in the south wall may have been added at that time. An octagonal font dated 1689 lies in the north porch. The north porch, considered of particular interest for its vernacular style, dates to the eighteenth century. The church was probably restored again in 1834 (the date of a date stone to the north of the west window). The bellecote dates to this time, and the west window and three windows in the north and south walls may also have been added then. The building underwent major restoration in 1899. It is thought that the present east window was inserted at this time. A new reredos was added, the pews replaced, the gallery removed, and the pulpit, choir stalls and reading desk rearranged. The octagonal oak pulpit was constructed from re-used fifteenth to late seventeenth century screen and box pew panels (the earlier with pierced tracery, the later with lozenge decoration). Seventeenth century pew panels were also used to re-panel the internal east wall. The font was replaced. An internal vestry was added to the west end. The roof was renewed in 1935. The church was further restored in 1976.

Sources include:
Beverley Smith, J, Beverley Smith, 2001, History of Merioneth II, 351-352
Cadw, Listed Buildings Database
Gwynedd Archaeological Trust, 2000, Historic churches of Gwynedd: gazetteer, 391

N Vousden, RCAHMW, May 2011