McMurphy, and its variants MacMurphy, Murphy and Murchison are anglicisations of the Irish language surname Mac Murchaidh.
The earliest reference to the name in Ulster occurs in 1172, when "Mulmaire McMurphy, lord of Munterbirn, was slain by Hugh Magennis and the Clan Hugh of the Iveagh of Ulster" (Maol Maire Mac Murchadha toiseach Muinntire Birn do mharbhadh la h-Aedh Mac Aenghusa agus la Cloinn Aeda do Uibh Eachdach Uladh).
They subsequently settled in the highlands of south Armagh, ousting families such as Garvey, Hanratty and Callaghan.
The townlands of Cashell and Legacroon in the barony of Orier were granted to McMurphy's c. 1610, but were seized by the time of Down Survey.
The Hearth Money Roll of the same year lists several bearers of the name in Dorsey, Legmoylan, and Creggan, though none in Carnally.