During archaeological excavations in the mid-1990s, carried out alongside restoration work on the castle itself, researchers uncovered fascinating evidence of this fortification's original design.

The excavation team discovered the foundations of what appears to have been a rectangular corner tower, located approximately 15 metres southeast of the main castle building. This structure, which would have formed part of the bawn wall; a defensive perimeter common to Irish tower houses; measured roughly 1.3 metres north to south and 2 metres internally. The discovery provides valuable insight into how the castle's defences were originally configured, with corner towers strengthening the vulnerable points of the enclosure.

Bawns were essential features of Irish castles and fortified houses from the medieval period onwards, serving as walled courtyards that protected livestock, stored goods, and provided a first line of defence against raiders. The presence of a corner tower at Kilcoe suggests a more sophisticated defensive arrangement than a simple wall, indicating the strategic importance of this coastal stronghold overlooking the waters of the bay.