Dromore Castle was probably constructed in the early 16th century. In the 17th century, Teige O'Brien of the O'Brien clan repaired and expanded it. The castle and lands of Dromore had been granted to Teige's father, Connor (Third Earl of Thomond), in 1579. Dermot, son of Teige, was an important protagonist in the Confederate Wars and participated in the Siege of Ballyalla Castle (Ennis). The last O'Brien at the castle was Conor, who left in 1689. The castle fell into ruin in the 18th century.