Kilmoremoy derives from the Irish Cill Mhóir Muaidhe, meaning the great church of the Moy, a reference to the River Moy that winds through this part of north Connacht. A place significant enough to be called the great church would have occupied a position of some importance in the early medieval ecclesiastical landscape of the region, though the precise nature of what now remains on the ground is not fully documented in available sources.

The parish of Kilmoremoy centred historically on the area around Ballina, which sits at the tidal reach of the Moy. Early Irish church sites of this type were often established between the sixth and ninth centuries, frequently associated with a founding saint or monastic community, and their remains can range from substantial stone ruins to little more than a graveyard enclosure marking where a building once stood. The Moy valley was well settled in early Christian times, and a church of such named prominence would likely have served a wide rural territory before later medieval reorganisation reshaped parish boundaries across Connacht.