The south wall of the medieval parish church, dedicated to the Holy Trinity, survives to a maximum height of only 1.5 metres on its north face and is almost invisible at ground level on the south. It runs for roughly 32.4 metres, sits about 10 metres south of the later church, and is not even quite parallel to it, that slight misalignment giving some sense of how thoroughly the two buildings belong to different worlds. In the south-west corner of the graveyard, a limestone mullion with chamfered glazing grooves and bar holes, along with a possible jamb bearing a hollow moulding and chevron carving, have been gathered together; architectural fragments that likely originated in a medieval window, perhaps what is known as a switchline window, a type with intersecting tracery.

The history attached to this site is unusually well documented for a parish church in County Limerick. The place-name Rathguala appears in the Book of Rights before 900, and by 1223 the settlement was in the hands of Keynsham Abbey in Somerset. The church itself was granted to the diocese of Limerick in 1228 by Roger Waspayl, who had also obtained rights of free warren over the land by 1252. Ownership passed through several hands over the following century and a half, including the Maltravers and later Mautravers family, and by 1369 an inquisition confirmed it as part of Iniskefty Manor. In 1318 the church was robbed by one A. Keating, a detail preserved in the Plea Rolls of Edward II. The dedication to the Trinity is confirmed by records dating to before 1410, and the whole settlement was burned in 1579 by the English governor Sir Nicholas Malbie during the Desmond rebellions. The 19th-century church that now occupies the same site was built in 1831 under the Board of First Fruits, a Church of Ireland body that funded the construction of hundreds of Protestant churches across Ireland in the early 1800s, and it retains a monument to Sir Thomas Southwell dating to 1676.

The church is approached through cut limestone piers flanking a cast-iron double-leaf gate, with steps leading up from the road; the ground level around the east and south of the building is raised and retained by rubble stonework, which itself hints at the accumulated archaeology beneath. The medieval wall is fragmentary and overgrown, so visitors looking for it should head south of the 1831 nave and look carefully along the ground. The architectural fragments in the south-west corner of the graveyard are easier to locate and reward close inspection, particularly the chevron carving on the possible jamb, a decorative form more commonly associated with Romanesque stonework. The graveyard also contains a variety of carved stone grave markers that span a considerable period.