Castlemartyr was incorporated by a charter of 1676, 26 Chas II, with a portreeve, two bailiffs, 12 burgesses and freemen. Castlemartyr was the home of Speaker Boyle and his branch of the family, and their control over the borough was unquestioned. Richard, 2nd Earl of Shannon, received the £15,000 compensation for its disfranchisement in 1800.