The Irish version of the surname is Mac Fhlannchaidh, from the personal name Flannchadh, which it is thought meant red warrior. It originated in two different areas in countries Clare and Leitrim. In the former they were a branch of the McNameras where their eponymous ancestor being Flannchadh Mac Commara.  The Clancy's formed part of the great Dai gCais tribal group and acted as lawyers or brehons to the O'Brien chieftains. Their homeland was in the barony of Corcomroe in north Clare and they remained prominent among the Gaelic aristocracy until the collapse of that institution in the seventeenth century. The Leitrim family of the name were based in the Rosclogher area of the country around Lough Melvin. Today the surname is still common in Leinrim and Clare with significant numbers also found in the adjacent countries.