The first documentary reference to St Trillo's Church dates to the thirteenth century. It is situated within a curvilinear churchyard, with Llandrillo High Street forming its northern boundary. The churchyard is surrounded by roads on all sides, and is some 30m west of the river Ceidiog. The churchyard wall was completely rebuilt during 1885-1877 restoration works. The oldest gravestone is dated 1676. A holy well, Ffynnon Trillo (NPRN 32388) was formerly located some 420m north of the church, and is depicted on modern and historic (1890-1901) Ordnance Survey mapping. The area to the west of the church is depicted on modern and historic (1890-1901) Ordnance Survey mapping as Tre'r-llan, which may indicate the presence of a former bond settlement associated with the church. A thirteenth century consecration stone (NPRN 275899) is located within the church. It was removed from Blaen Cwm, Llandrillo in 1960, and its latin inscription is now largely illegible.

The church is a Grade II listed building and consists of nave and chancel, south-east transept and vestry, south-west tower and north-west porch. Unusually, it is not built on an east-west axis, but is aligned thirty six degrees north of an east alignment. A sixteenth century font was returned to the church from the vicarge garden in 1960. The pre-1776 church was noted to consist of a single aisle measuring forty yards in length and ten yards breadth, with a strong, graceful tower and two bells. There were two south doors and one north door. The chancel and nave were divided by a decorated rood screen and loft, with carved vine trail, dragons, lions, roses and interlacing. The church was rebuilt in 1776, on the footprint of the medieval building. The church was restored in 1852. By 1865 the loft had been removed to form a west gallery, although the screen was still in existence. At this time there was west door through the tower. The church was rebuilt in1885-1887, due to extensive cracks at the east end of the north-west wall. The nave was largely replaced, along with all windows. A porch, chancel and vestry were added, and most of the fittings were replaced. The tower was renovated, with the west door being blocked and a new arched opening inserted.

Sources include:
Beverley Smith, J, Beverley Smith, 2001, History of Merioneth II, 362-363
Gwynedd Archaeological Trust, 2000, Historic churches of Gwynedd: gazetteer, 391
www.llandrillo.demon.co.uk/llandrillo/parishchurch/index

Nikki Vousden, RCAHMW, 9 June 2012