The single-cell church, roughly 12.9 metres east to west and 6.65 metres north to south, retains a surprising density of internal features: a piscina, the shallow stone basin set into the wall where a priest would rinse the chalice after Mass, with its drainage channel still visible; multiple aumbries, small recessed wall cupboards used to store sacred vessels; and an east window of twin ogee-headed lights whose glazing grooves show where wooden shutters were once held shut with a drawbar. At the west end, a residential tower, wider than the church itself, rises above a barrel-vaulted arch. The vault was constructed using wicker centring, a method by which woven rods formed a temporary mould over which the stone was laid, and traces of the original plaster finish survive on the underside. The arrangement is unusual: because the east wall of the tower was left open, the vaulted arch creates an undivided undercroft that flows directly into the church floor.

The building has two distinct historical voices. Writing in 1682, Sir Henry Piers described Templecross as a small but well-built chapel in good repair, with a single bell that had, as he put it, the good fortune to escape the fury and rapine of the late war. He noted that it had served as a venue for ordinations under a former Bishop of Meath, standing in for the ruined mother church at Kilbixy. By 1826, the picture had reversed entirely: a visitor recorded the chapel as already in ruins, though still identifiable as the place where the Piers family kept their sepulchral vault. That family connection runs deep. An armorial plaque on the south wall, which partially blocks one of the church's original windows, bears an inscription crediting Sir Henry Piers, in the late sixteenth or early seventeenth century, with renovating the building, inserting a fireplace and chimney stack into the tower, and constructing the road that led to it. The chest tomb of the Piers family sits alongside the plaque, the window behind it half-obscured by their memorial.