Tarmon Castle was built by the O’Connor Kerry clan, an influential Gaelic family who controlled much of north Kerry from their main stronghold at Carrigafoyle. The O’Connors were strategic in their territorial control, constructing smaller fortifications at Asdee and Tarmons to extend their influence across the region.

The castle’s history is closely tied to the establishment of a new lordship within the O’Connor Kerry dynasty. John O’Connor, seeking to provide for his second son Dermot, created the Lordship of Tarbert and likely built Tarmon Castle as its seat. Historical records indicate that by 1550, the 3rd Lord Tarbert was residing at the castle, suggesting it had been the family’s residence for at least two generations prior. This branch of the O’Connor Kerry clan would have used the castle to administer their lands, collect rents, and maintain their authority in this part of Kerry.

Today, nothing remains visible of Tarmon Castle above ground. The site, recorded in archaeological surveys but showing no surface traces, serves as a reminder of how completely some medieval structures can vanish from the landscape. Like many Irish tower houses and castles that fell into disuse after the 17th century, Tarmon Castle has been reclaimed by the earth, its stones likely repurposed for local building projects over the centuries. The castle’s story survives only in historical documents and the archaeological record, a testament to the once powerful O’Connor Kerry lords who shaped this corner of Ireland.