St Tydechno's Church was first mentioned in documents of 1254. St Tedecho's, Llanymawddwy shares its dedication with St Tydecho's, Mallwyd (NPRN 43907). Llanmawddwy is the principal church, with Mallwyd being its subsidiary chapel. Together the two parishes formed the commote of Mawddwy, which did not become part of Merioneth until 1536. The church is situated within a large churchyard, whose west side is curvilinear. It is bounded by a road on the south-west side, which is also curvilinear. There is a modern lych gate in the south boundary. A graveyard chest tomb, known as 'Garreg Offrwm' is situated outside the east wall of the church (NPRN 310292). The tomb was erected in 1790, and was used for the ancient custom of the payment of funeral offerings.

The church is a Grade II listed building, built of rubble stone. It consists of a nave with bellcote, chancel and south porch. The octagonal font with scalloped decoration is medieval, and currently sits on a millstone. A plinth at the foot of the west wall, and the section of the south wall below sill level are thought to be medieval. It is thought that the present building was largely rebuilt in the nineteenth century. All the windows, the doorway, chancel arch and roof timbers are modern.

Sources include:
Beverley Smith, J, Beverley Smith, Ll, 2001, History of Merioneth II, 364
Gwynedd Archaeological Trust, 2000, Historic churches of Gwynedd: gazetteer, 391

N Vousden, RCAHWW, 5 July 2012