The main O'Sullivan Mór familial seat moved to nearby Cappanacush Castle during the 17th century, and antiquary Samuel Lewis noted that both castles were "traditionally said to have been defended" by their O'Sullivan Mór owners during the mid-17th century Cromwellian conquest of Ireland. The O'Sullivan castles and lands at Dunkerron and Cappanacush were confiscated following this conflict under the Act for the Settlement of Ireland 1652, and assigned to Cromwellian supporter William Petty. Later O'Sullivan attempts to have the lands returned were not successful.