St Tecwyn's Church is thought to be medieval in origin. An eleventh century inscribed stone is incorporated into the present church building. The inscription has been interpreted as 'the Cross of St. Tecwyn, presbyter, to the honour of God and the most illustrious servant of God, Heli, deacon, made me. (the last word may read 'merci')'. Another medieval stone, whose pattern includes a linear Latin cross with a lozenge shaped ring at its upper end, is one of only four definite examples in Wales. The other examples occur on stones at St David’s Church, Llanllawer (NPRN 308778), St Sulien's Church, Silian (NPRN 402554) and St Tanwg's Church, Llandanwg (NPRN 43901). St Michael's Church, Llanfihangel-y-traethau (NPRN 43894) was formerly a chapel dependent on St Tecwyn's, Llandecwyn.
The churchyard is curvilinear and opens off a track way which was once the main county road to Maentwrog, and has been suggested to be Neolithic in origin. It is reputed to have been associated with 'Maen Tecwyn', which is said to have been blown up some years before 1914, and its fragments used in the building of a barn. The lych gate, thought to be seventeenth or eighteenth century, is located at the west end of the south wall. The churchyard is encroached by a seventeenth century cottage on its south side. When the church was restored in 1879-1880, an inscribed stone was found some ten to twelve feet from the west end. Its measurements are given as fourteen inches length x two inches breadth, with a height decreasing from four inches at one end to two and a half inches at the other. It bears a four line Latin inscription, thought to date to the eleventh century. In 1905 the stone was noted to be at Llanfihangel-y-traethau vicarage.
The medieval church building is described as an ancient structure, in the early style of English architecture, with a gallery at its west end. Its measurements are given as eighteen yards length x five yards width.
The present church is a Grade II listed building, constructed of rubble stone. Erected in 1879-1880, it is thought to have been built immediately to the north of its predecessor, and to incorporate elements of the medieval structure. The building consists of a continuous nave and chancel, with a south porch and western bellcote. A recess on the south side of the chancel may be a re-set medieval feature. A slate memorial dating to 1706 is re-set in the eastern-most buttress of the south wall.
Beverley Smith, J, Beverley Smith, Ll, 2001, History of Merioneth II, 348
Edwards, N, 2007, A Corpus of early Medieval Inscribed Stones and Stone Sculpture in Wales: Volume II
Gwynedd Archaeological Trust, 2000, Historic churches of Gwynedd: gazetteer, 391
N Vousden, RCAHMW, 1 May 2012