Rising to about eight metres on its western face, this structure, attached to the main body of the church, was in all likelihood a priest's residence, entered through a pointed doorway set into the gable wall. It is an unusual survival, the kind of domestic addition that rarely makes it into descriptions of ecclesiastical ruins, and its presence here gives the site at Dromin South a slightly layered quality, as though several different centuries of use have been quietly folded into one another.

The antiquarian T. J. Westropp, writing in 1904 and 1905, set down the details that allow us to read this place with some precision. The church itself measures roughly fifteen and a half metres by just over six metres, with walls around four metres high and three quarters of a metre thick. The east window is oblong, fitted with a horizontal cross-bar and a flat-arched splay, and there are five side-lights in total, three to the north and two to the south. Medieval records name the settlement variously as Dromin Claryn in 1291 and Dromin Icherolyn in 1302, and a map from 1410 confirms the dedication to the Holy Trinity. The place-name itself carries older information still: it derives from the Irish for "little ridge of the O'Clerens," referring to the O'Cleirchens, who were sub-chiefs of the Uí Cairbre Aodha. By 1296, one Almerica de Bellofago was pursuing a financial claim against the settlement, and in 1325 a certain R. de Burgo held it on behalf of Peter de Colgan and the Earl of Kildare, suggesting the site passed through several layers of medieval lordship.

The ruins sit within Dromin graveyard, which remains in use and provides the easiest point of orientation for a visitor. The church walls are still largely standing, and the western residential tower, despite having its south wall levelled, gives a reasonable sense of its original height. To the south-west, in the townland of Ballynamuddagh, lies Trinity Well, a holy well, that is, a natural spring with religious associations, sharing the same dedication as the church. The two sites together suggest a small but coherent medieval sacred landscape that has persisted, in fragmentary form, into the present.