The surname Poer (also Poher, Puher: the earliest references omit the prefix le. The modern form is, of course, Power) seems to have denoted a native of Picardy in northern France, although a connection with the district of Poher in Brittany has also been suggested and a multiple origin is possible. A number of bearers of the name, members of a family associated with the de Courcys in Somerset and Devon, figured prominently in the invasion of Ireland from 1170 on. Robert Puher, a member of the household of King Henry II, whom he accompanied to Ireland in 1171, was appointed governor of Waterford in 1177. It is probably the same man who had acquired Dunshaughlin and Ratoath in County Meath before 1191. Others were Roger (killed 1188), William and Reginald Poer, while Simon le Poer was briefly (1185-90) lord of half the "kingdom of Cork" as husband of Milo de Cogan’s daughter and heiress Margaret.
Descendants of some of these Poers certainly endured in County Kilkenny, and it is possible that Henry Poher, to whom King John granted the great barony of Dunoil (Dunhill) in County Waterford belonged to this family, but the fact that a charter of his begins with the formula "to all my men: French, English, Welsh and Irish" suggests rather an origin in the Welsh marches, where the surname also occurs. Henry’s grandson, John fitz Robert le Poer of Dunoil (dead by 1242), acquired also lands in Limerick and Connacht, but the lineage remained overwhelmingly connected with County Waterford and the surrounding areas. John’s son, another John, produced King John’s charter in court in 1262, but unfortunately the text does not survive. By 1300 the Poers were one of the most numerous of the "Anglo-Norman" lineages and included a substantial criminal element. One branch bore the strange epithet of the "blackman" Poers, while conversely Sir John fitz William le Poer (died 1295) was known as "the white Poer." He founded the County Cork branch of the family. In the 1320s the family were involved in a bitter feud with Maurice fitz Thomas, first earl of Desmond. The direct line of the barons of Dunoil comes to an end shortly before 1360, an event followed by bitter internal feuds within the lineage.
Sir Eustace fitz Benedict le Poer (died 1311) the younger son of a junior branch, was a remarkable self-made man who, having married a rich widow, built up an enormous landed estate, including the great barony of Kells in County Kilkenny. He died childless, having divided up his lands among his kinsmen. His nephew, Sir Arnold fitz Robert, seneschal of Kilkenny, died in 1328 in Dublin Castle, where he had been imprisoned on a charge of heresy through his involvement in the famous Kilkenny witchcraft case. His son, another Sir Eustace, having taken part in the rebellion of his family’s former enemy, the earl of Desmond, was captured in County Kerry in 1346 by the chief governor, Sir Ralph Ufford, and executed, his lands being confiscated. Nicholas fitz John le Poer of Kilmeaden (died after 1393), the largest landowner of the lineage in his day, was a nephew or grandnephew of Sir Eustace fitz Benedict, some of whose lands he inherited. He was the ancestor of the later Kilmeaden line, who in the fifteenth century also obtained possession of Dunoil itself. His rivals for the leadership of the lineage were Richard fitz John le Poer (died. 1376) and his son David Rothe (Ruad, "the red"). Around this time commenced the long and bitter feud between the Poers and their neighbors, the citizens of Waterford, which was to continue for a century and a half.
David Rothe’s son Nicholas, known patronymically as Mac Daibhid Ruaid, was appointed in 1425 to the sheriffship of County Waterford, an office that he and his descendants were, uniquely in Ireland, to convert into a hereditary lordship. He was a man of sufficient note for his death in 1446 to be picked up by an annalist in far-away Fermanagh. His son Richard (died 1483) succeeded him as sheriff, surviving a parliamentary attempt in 1476 by the citizens of Waterford to have him removed as a Gaelicized rebel, who used only "brehon" law. The sheriffship, converted into a local lordship over the eastern half of County Waterford, passed in turn to his son Piers and his grandson, another Richard (died 1539), who was raised to the peerage in 1535-1536 as Lord Power of Curraghmore, a title which remained with his descendants. His remarkable widow, Katherine Butler, was the last to exercise autonomous authority over "the Power Country."