In early medieval times the most important sept of O'Cahill was that located in Co. Galway near the Clare border, the head of which was Chief of Kinelea (Aughty), but by the middle of the thirteenth century their former position as the leading family in Kilmacduagh had been taken by the O'Shaughnessys. The name is uncommon there now, but is found in Co. Clare where a branch of the sept was also established. There were quite distinct septs of O'Cahill: one of these was located near Lough Leane in Kerry and another in Co. Tipperary between Thurles and Templemore. There are no less than three townlands called Ballycahill in Co. Tipperary which perpetuate the original habitat of that sept. Two other Ballycahills, one in Co. Galway, between Portumna and Killimor, the other in Co. Clare near Ballyvaughan, also indicate the location of those septs. To-day the great majority of Cahills are to be found in the three Munster counties of Tipperary, Cork and Kerry. In Irish the name is O Cathail, I.e. descendant of Cathal, a Christian name which, Dr. M. A. O'Brien informs me, is derived from the Old Irish catu-ualos meaning powerful in battle. Cahill is one of those surnames seldom if ever found in modern times with its proper prefix O. O'Cahill is one of the earliest surnames on record: Flann O'Cahill was martyred in 938. The most notable man of the name was that versatile priest Father Daniel William Cahill (1796-1864), schoolmaster, newspaper editor and prolific lecturer in the U.S.A. and elsewhere on behalf of Catholic institutions.