William Caulfeild, 1st Viscount Charlemont

William Caulfeild, 1st Viscount Charlemont PC (Ire) (1624 – April 1671), was an Irish politician and peer.

Background Born in Donamon Castle in County Roscommon, he was the third son of William, 2nd Baron Caulfeild, and his wife, Mary King, daughter of Sir John King and Catherine Drury. His two older brothers, Toby, 3rd Baron Caulfeild, and Robert, 4th Baron Caulfeild, both died without male issue and he succeeded to the barony on the latter's death in 1644.

Career Having been first a leading Parliamentarian under Oliver Cromwell, he captured Sir Phelim O'Neil in 1653 and executed him for rebellion and the murder of his brother Toby and his family. In 1660, the then Lord Caulfeild switched his allegiance and supported afterwards King Charles II of England, captaining a troop of horse.

Family In 1653, the then Lord Caulfeild married Hon. Sarah Moore, second daughter of the 2nd Viscount Moore of Drogheda and his wife, Alice Loftus, and had by her four sons and three daughters. She was the sister-in-law to Caulfeild's younger brother Thomas. He was succeeded in his titles by his second and oldest surviving son, William. married, firstly, John, son of Archbishop James Margetson and, secondly, the 1st Baron Carpenter.