Sweeney, along with its variants MacSweeny and MacSwiney, comes from the Irish Mac Suibhne, from suibhne, meaning "pleasant. The original Suibhne from whom the surname derives was a Scottish chief based in Argyle around the year 1200. His people were of mixed Viking and Irish descent, and their fame as fighters meant that they were much in demand in Ireland as gallowglasses, or mercenaries. Suibhne's great-great-grandson Muchadh Maer Mac Suibhne settled in the Fanad district of the modern Co. Donegal in the fourteenth century, and his offspring soon split into distinct groups, the principal ones being Mac Suibhne Fanad and Mac Suibhne na dTuath. The former, the senior branch, were based at Rathmullan and among their strongholds were Doe Castle and Rahan Castle. For over three centuries, up to the final defeat of the seventeenth century, they fought as gallowglasses in the struggles of Ulster, mainly on behalf of the O'Donnells. Members of both groups also made their way south to Cork in the late fifteenth century and served the MacCarthys, acquiring territory of their own in Muskerry. The Cork family prospered and multiplied, and today the surname is more numerous in the Cork/Kerry area than in its original Irish homeland of Ulster.
.John Swiney took part in the 1798 rebellion and Emmett?s rising in 1803, after which he escaped to Normandy, where the family still exists. Another Cork patriot was Terence MacSwiney (1879-1920), the Lord Mayor of Cork who died on hunger strike in prison in 1920. Thomas William Sweeney was a general on the Northern side during the American Civil War and a member of the Fenians. James J. Sweeney ( 1900-86) was a Director of the New York Museum of Modern Art and a renowned art historian and critic. Patrick Valentine MacSwiney was created a Roman hereditary marquis in 1896. He took part in the 1916 rising and later helped in the creation of the Irish diplomatic service.