This is a very unusual Irish surname. Recorded as McChesney, and more often Chesney, and sometimes in County Cork as Chaney, it is generally to be found in the province of Ulster in Northern Ireland. It is a rare example of a Gaelic form of a French invaders name. The Chesney's originally went to England with the invasion army lead by William, Duke of Normandy in the year 1066, when he conquered the country. Later they received large land grants in the counties of Sussex and Kent, for their support. The surname originates from the villages of Le Quesnay in the French departements of Calvados, Seine-Inferieure, and La Mauche, and means the place of the Oak Trees, for the original ches-nai. The surname made its first appearance in Ireland with that of Ralph de Chaeny, given as being the Seneschal of the province of Leinster in 1246, some seventy years after King Henry 11nd of England conquered most of Ireland in the year 1170. It would seem that at some point in history some of the Chesney's sided with their "new" Gaelic neighbours and adopted the Mac prefix as a sign of their changed allegiance. The first recorded spelling of the family name is shown to be that of Radulfus de Caished. This was dated 1086, in the Domesday Book of Sussex, during the reign of King William Ist of England, 1066 - 1087. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.