The English surname Moon, also found in Ireland, is an habitational name from Moyon in La Manche, named from the Gallo-Roman personal name Modius (from Latin modus meaning “measure”.) When found in Ireland the name Moon is an anglicized form of the Gaelic name Ó Mocháin. The first name holder was one William de Moion, a close follower of Duke William of Normandy, and one who after the famlous Conquest of 1066, was granted various estates in the county of Dorset. Other early examples of the surname from this source include: Reginald de Moyn of Somerset in 1239, and William de Mohun of Wiltshire, in 1272. William Moon settled in Virginia in 1637 and today there are approximately 42,000 bearers of the name Moon living in the United States.