Roughan Castle is a State Care Historic Monument in the townland of Roughan a mile outside Newmills. It was built about 1618 by Sir Andrew Stewart, 2nd Lord Castlestewart, eldest son of Andrew Stewart the third Lord Ochiltree, 1st Lord Castlestewart who came from Scotland during the plantation and established the nearby town of Stewartstown. Andrew Stewart junior acquired the land of Ballokevan from Robert Stewart between 1610 and 1619 and built his castle overlooking Roughan Lough. It is a small square castle, three storeys high with a central tower 20 feet square, flanked by thick rounded towers at each corner. The castle was once the refuge of Phelim O'Neill, leader of the Irish Rebellion of 1641 in Ulster. He was captured there in 1653 and taken to Dublin, where he was hanged for treason.