 The first church on this site was established by Cwyllog, a female saint, in the 6th century, although the exact date is unknown. She was one of the daughters of St Caw, a king in northern Britain who lost his lands and sought safety with his family in Anglesey, where the ruler Maelgwn Gwynedd gave him land. There was a church here at the time of the Norwich Taxation in 1254, and the present walls may date from around 1200. In the 13th century, the church was under the control of the Augustinian canons of the priory at Penmon, on the east of Anglesey, with the priory gaining the income from the tithes paid to the church. The priory gradually diminished in size and importance, and in 1522 the prior and two canons (the entire community, at that stage) affixed their signature to the lease of Llangywllog church to Richard Bulkeley (a member of a prominent family from the Anglesey town of Beaumaris) for the period of 100 years at an annual rent of £ 1.
