Cusack is an Irish family name of Norman origin, originally from Cussac in Guienne (Aquitaine), France. The surname died out in England, but is common in Ireland, where it was imported at the time of the Norman invasion of Ireland in the 12th century.
While not a particularly common name, Cusack is historically associated with a number of variant forms, such as de Cussac, de Cusack, de Ciusak, de Cíosóg, de Ci'omhso'g, Mac Iosog, and Mac Isog.
Irish emigrants to America were reportedly given alternative spellings by immigration officers, based on their pronunciation, however this appears to be a myth. The following: Cusack, Kuzak, Kuzack, Cusick, and Cussack are modern variants.
Read more about Cusack: Origin, History, Plunder & Ransom, Occupational Summary, Killeen Castle, Llanthony, Biltini Manor, Dunsany, Crest, Motto, Memorial Stones, Lady Joan De Cusack, Notable Modern Cusacks