[3] St Cwyllog's Church is in a rural location in the middle of Anglesey, about 3 miles (5 km) north-west of Llangefni, the county town, and a short distance from the small village of Llangwyllog.

[5] The first church on this site was established by Cwyllog, a female saint, in the 6th century, although the exact date is unknown.

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.

[1] The church is built from rubble masonry with very large boulder quoins; the roof is made from slate with stone copings.

[3] The church has a cylindrical stone font dating from the 13th century, carved with decorations, particularly an elaborate leaf design and a knotwork pattern.

[9] The altar has communion rails on three sides, which are probably of similar date to the pulpit, and seats nearby in the chancel on the north and south walls.

Further investigations showed that it had once belonged to a nearby closed church that had transferred its silver to St Cwyllog's.

[3] The 19th-century antiquarian Angharad Llwyd described the church as "small, but remarkably well built", and mentioned the "ancient and curious chapel at the west end of the nave.

"[13] Writing in 1859, the clergyman and antiquarian Harry Longueville Jones said that St Cwyllog's had "rather better architectural features about it than most of the small churches in Anglesey.

"[14] A 2009 guide to the buildings of the region describes the 1854 restoration as "tactful", and notes the "rare surviving Georgian fittings", including the pulpit.

[10] A 2011 guide to the religious buildings of Wales says that St Cwyllog's has "the earliest and finest of several pre-ecclesiological church interiors in Anglesey".