What makes Kilmactalway stranger still is the earthen bank running against the inside of the enclosure wall, a feature that suggests this circular boundary predates the church itself and may mark an early ecclesiastical enclosure, a type of boundary used in early Christian Ireland to define sacred or monastic ground. The church survives almost to eaves height, roofless but largely intact, and the graveyard remains in use.

The church was dedicated to St. Magnenn, as recorded by Mason in 1820 and confirmed by Ronan in 1941, though the origins of the dedication reach back much further. In 1366 the parish was annexed to St. Patrick's Cathedral in Dublin, drawing it into the orbit of the city's ecclesiastical administration. Records from 1615 and 1630 noted the nave and chancel as being in good repair, and the building was subsequently rebuilt, as Ball recorded in 1906. What stands today is a structure of roughly coursed limestone, with hammer-dressed quoins at the northeast and southeast corners and a pronounced batter, a deliberate outward slope, at the base of the east wall, a detail often used to add structural stability. The interior, measuring just over sixteen metres long and five metres wide, is entered through a narrow pointed doorway in the south wall, and there is a step down into the space. Windows vary notably in style: an ogee-headed window lights the west gable, which also carries a double bellcote; a two-centred arched window with granite jambs and bar holes sits in the south wall; and the east wall holds a small round-headed lancet set in a deep embrasure with a granite and limestone internal ledge. A baptismal font once stood somewhere in the graveyard, documented by D'Alton in 1838, but it had already disappeared by the time Ní Mharcaigh surveyed the site in 1997.

The church sits in a rural setting surrounded by farmland, and the circular enclosure wall is the most immediately legible feature from the approach. The interior repays close attention: the mix of window types reflects different phases of construction or insertion, and the bar holes in the south wall window, designed to hold iron bars across the opening, are a small but telling detail of how such spaces were once secured. The graveyard is still active, so the site is generally accessible, though the ground is uneven and the step down into the church shell requires care.