The origins of present-day Crossmolina are tied to the founding of a religious settlement in the area: Errew Abbey was founded by St. Tiernan in the 6th century. In the 12th Century this Abbey came into possession of the invading Hiberno-Norman de Barry family. During the 15th century, Crossmolina passed into the hands of the Bourke Family. In 1526 O'Donnell of Tir Conaill (Co. Donegal) invaded Tirawley and destroyed Crossmolina Castle. In response, the Bourkes constructed a replacement in Deel Castle. Their possession of this new fortress did not last however as during the Williamite War in Ireland of the 1690s Thomas Burke fought for the defeated Catholic Jacobites. Subsequently, Deel Castle was granted by the English crown to the Anglo-Irish Protestant Gore family, ushering in the era of Protestant Ascendancy into the area.