The walls and gables of this small single-cell building are almost entirely intact, its west gable now braced by a brick and concrete flying buttress, while the surrounding graveyard that once enclosed it has long since disappeared beneath tarmac and front gardens. One of the windows embedded in the south wall does not even belong to the building; it was salvaged from an entirely different church on the other side of the city and inserted here around 1900.

The church is known locally as Old Church or St Munchin's Church, and its full name, Kilrush, appears in the historical record under various spellings, including Kellros, Kelleroisse, and Kylros in the medieval Black Book of Limerick. It was reputedly founded by a woman named Rose, said to be the sister of St Munchin, the patron saint of Limerick Diocese. By 1302 it was listed in the Ecclesiastical Taxation of the Diocese of Limerick, valued at ten shillings per annum. The building itself is constructed of large, well-coursed rubble set on a protruding plinth, entered through a flat-headed trabeate doorway, a type in which the opening is spanned by a single horizontal stone lintel rather than an arch, in the centre of the west gable. The east gable holds a round-headed window set into a semi-circular arched embrasure. The south wall carries the transplanted piece: a late medieval window with chamfered limestone jambs, holes for glazing bars, and a Gothic lettered inscription associated with the Quinlivan family, removed from the Franciscan friary in St Mary's Lane in the city and preserved for a time by a Robert Vere O'Brien before being set into the wall in its present position. A blocked doorway in the north wall, with evidence of red brick at its base, appears to be a post-1700 insertion.

In 1980, ahead of housing construction on the site, Larry Walsh, then curator of Limerick Museum, opened six excavation trenches across the development footprint. The dig uncovered 39 burials, the majority clustered on the south side of the church near the Quinlivan window. Over forty per cent of those identified were infants, pointing to the likely presence of a cillín, an informal children's burial ground of the kind found across Ireland, probably in use during the post-medieval period. The church is a designated National Monument, subject to a preservation order since 1937. It is accessed off Old Church Road, about two kilometres south-west of Thomond Bridge and roughly 155 metres north of the Shannon, sitting quietly between the houses that now surround it on all sides.