By the time of the publication of a guide to the churches of Anglesey in 2006, the church had been closed for some years and the windows boarded up; it was noted that the fabric was still in generally good condition. The church is built from rubble masonry dressed with freestone, and it has a slate roof, with a bellcote at the west end and stone crosses on the porch and chancel roofs. The timbers of the roof can be seen from inside. The walls have been assessed as being "probably not older than the fifteenth century". There is no internal division between the nave and the chancel, and the church as a whole is long by wide. The porch, at the west end of the south wall, was added in the late 19th century. There is one window in the north wall and two in the south wall, all of which are single windows set in rectangular frames; the east window has a pair of lights (vertical sections of window separated by a mullion). All the windows date from the late 19th century. The plain bowl-shaped font dates from the 12th century. There is a brass memorial plaque recording three people who died in the 1640s. The 1937 survey by the Royal Commission on Ancient and Historical Monuments in Wales and Monmouthshire recorded that the church possessed a silver cup from 1630 and a salver dated 1784–85. The churchyard contains some gravestones, including a few dating from the 1980s and 1990s. The church has national recognition and statutory protection from alteration as it has been designated as a Grade II listed building – the lowest of the three grades of listing, designating "buildings of special interest, which warrant every effort being made to preserve them". It was given this status on 12 May 1970, and has been listed as "a simple, rural Medieval church". Cadw (the Welsh Assembly Government body responsible for the built heritage of Wales and the inclusion of Welsh buildings on the statutory lists) also notes that it retains "much of its original vernacular character", despite the 19th-century alterations. Writing in 1861, Harry Longueville Jones said of St Peirio's that it was "one of the humblest ecclesiastical buildings in Anglesey". He said that there were "no architectural features in this church worthy of delineation."