For background on how the map was made (and its flaws), see the relevant blog entry.
|Cahill||Very numerous: all provinces but least in Ulster. Ir. Ó Cathail, a very popular personal name in early Ireland (see entry). There were septs in Clare, Tipperary and Kerry. It is one of the earliest surnames on record. IF & SGG.|
|MacCahill||fairly rare: Donegal-Tyrone-Cavan. Ir. Mac Cathail from first name Cathal meaning "strong in battle". May also stand for Mac Cathmhaoil (battle chief).|
|Ó Cathail||Cahill: an-líonmhar ar fud na tíre: Clanna móra sa Mhumhain agus i gConnachta. Ainm pearsanta is ea Cathal a chiallaíonn "calma sa chath".SGG.|