St Cadfan's Church is situated within a rectilinear churchyard, whose south and east boundaries are delineated by roads. The southern churchyard wall was originally curvilinear, but was rebuilt in 1908 to accommodate road widening. The current churchyard appears to have once been part of a larger curvilinear enclosure, dilineated by south and east churchyard boundaries, Gwalia Road to the north-east and a stream (immediately north of St Cadfan’s Wells) to the north. The site of Ffynnon Gadfan, later St Cadfan's Wells (NPRN 32397) is located some 150m to the west-north-west of the church and in 1535, St Cadfan's well was noted to lie within the churchyard. The well reputedly cured rheumatism, scrofula and cutaneous disorders. Four early medieval inscribed stones are associated with the church. Tywyn 1 (now lost) was first noted in 1698, when it stood in the churchyard, to the south-east of the Church. Its Roman inscription is thought to be fifth century in date. Tywyn 2 (NPRN 302689), thought to be ninth century in date, presently stands upright in the north aisle of the church. It bears the earliest known inscriptions in Welsh. Tywyn 3 (NPRN 302689), a seventh to ninth century cross-inscribed pillar-stone, is thought to have been found buried at Bryn Paderau (Pater Noster Hill) some 500m south-south-east of the church, at the point where it first comes into view. Modern Ordnance Survey mapping depicts the road connecting the two sites as 'Ffordd Cadfan'. The stone is thought to have possibly been a boundary marker associated with church land and was built into the tower (below the belfry window) in 1884. Another possible (uncarved)boundary stone, Croes Faen, stands adjacent to the roadside some 1km north-east of St Cadfan's Church. Tywyn 4 (NPRN 419550) is currently located inside the church building, at its west end near Towyn 2. It was first noted in 1986 after the demolition of Ynysmaengwyn mansion (NPRN 54223), where it had been built into one of the outhouses. Originally a sundial dating to the eighth or ninth century, it is thought to have been associated with the church. The first documentary reference to St Cadfan’s Church was in 963, when it is thought to have been the mother church of the region. A twelfth century poet, Llywelyn Fardd, reportedly described the church as a whitewashed building with a ditch surrounding it, beyond which was a clas or lay community, dependent on the church. The poet also emphasised the refuge and territorial protection conveyed by St Cadfan (and hence, by association, the church). The church was a place of pilgrimage at that time, where relics were reportedly kept and miracles performed. A chantry chapel is documented as having been situated in the north-west of the churchyard. The present lych gate (NPRN 419547) is Grade II listed and dates to 1908.
The cruciform church is a grade I listed building. It consists of aisled nave, north and south transepts, central tower and chancel. The nave, with its aisles, arcades and clerestory windows, are those of the original twelfth century building. The nave is unique in Gwynedd and is consequently considered to be of special architectural significance. Three bays remain of an original four. The arcades both have three massive, squat, drum columns from which spring plain rounded arches. The clerestory has small, deeply splayed, round-headed windows above the columns. The arch-braced roof of the nave dates to the fourteenth century. The octagonal font is also thought to be fourteenth century in date. Two fourteenth century effigies are situated within modern niches in the north wall of the chancel and sanctuary. One of the effigies is of an unnamed priest. The other is of an unnamed knight, traditionally Gruffydd ab Adda of Dolgoch. The original tower collapsed in 1692 and was replaced with a tower over the west end of the nave. The present character of the church owes much to an extensive program of rebuilding, modernisation and other alterations, completed in 1884. It was at this time that the 1792 tower was removed and replaced with the present tower. A new west wall was built, excluding the previous fourth bay of the nave. A new south door and aisle windows were also added. The present chancel was built at this time, although it is thought to have been built on the foundations of its predecessor.
Beverley Smith, J, Beverley Smith Ll, 2001, History of Merioneth II: The Middle Ages, 368-70
Edwards, N. 2013, A Corpus of Early Medieval Inscribed Stones and Stone Sculpture in Wales: Volume III North Wales
Gwynedd Archaeological Trust, 2000, Historic Churches of Gwynedd: Gazetteer, Report 391
Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 630.
N Vousden, RCAHMW, 20 July 2012