The O prefix has long since been dropped. It is Ó Deasmhumhnaigh in Irish, denoting descendant of the Desmondman, the old name of south-west Munster (deas, south; Mumha, gen, Munihan, Munster). O'Deason was an early form in English. It has always been closely associated with Co. Cor. . It was presumably acquired by imigrants from Desmond to the northern and eastern parts of Co. Cork, the country around Mallow was its main habitat. Kingwilliamstown, in the Newmarket district of Co. Cork, has of late years been renamed Ballydesmond. The surname appears in 1659 as MacDesmond in the list of principal Irish names in the barony of Kinalea, Co. Cork. Possibly confusion on the part of Petty's enumerators between the prefixes Mac and 0. Desmond, when used as a title not as a surname, is one of the most prominent names in Irish history on account of the leading position of the southern branch of the Fitzgeralds, of whom between 1329 and 1583 fifteen were Earls of Desmond.