Browne Willis and A.W. Wade-Evans agree on the dedication of the church, although there is no clear evidence for the dedication prior to the eighteenth century.

However, the number of local features and a lost chapel (capel tydacho) in the churchyard point towards Llanymawddwy being at the centre of a cult to Tydecho in the Middle Ages. Tydecho is praised as 'a holy man ... from Mawddwy' in a fifteenth-century poem by Dafydd Llwyd of Mathafarn, which underlines the likelihood that the dedication of the church is much older than the eighteenth century.

Buches Dydecho (Tydecho's Milking Fold) is located on Fridd y Glasgoed, or Llaethnant, about two and a half miles north-west of Llanymawddwy, near the source of the River Dyfi. Further landscape features in te area included Gwely Tydecho, Ffynnon Dydecho and Cadair Dydecho.