Sir John MaCoghlan built Coole Castle on the banks of the Brosna in 1575. It was the last of the MacCoghlan castles to be built. He erected it as a present to his second wife Sabina O’Dallachain. Formerly, there was a mural slab in the castle with a Latin inscription translated in English as ”“This tower was built by the energy of Sir John MacCoghlan, K.T. chief of this Sept at the proper cost of Sabina O’Dallachain on the condition that she should have it for her lifetime and afterwards each of her sons according to their seniority”.
The whereabouts of the mural is unknown at present. In his will in 1590, Sir John left Coole Castle to his widow. Over the fireplace, in its original location, in the topmost room of the castle is a plaque written in Middle Irish which reads: