De Moirtiméir
de MOIRTIMÉIR—XI—de Mortimer, Mortimer, etc. Norman 'de Mortemer,' i.e., of Mortemer in Normandy; incorrectly Latinised 'de Mortuo Mari' (of the Dead Sea), for which reason it was supposed to have arisen in crusading times. One of the de Mortimers accompanied William the Conqueror to England, and the name appears in Domesday Book. It came into Ireland about the time of the Anglo-Norman invasion. In 1185 Robert de Mortemer was witness to King John's Dublin Charter. The family settled in Meath, but was never very numerous.
Alphabetical Index to Irish Surnames