In the late 1990’s my father replied to an advertisement in an Irish magazine for information on the family’s history and coat of arms. He received a stylized document which he framed and hung on the wall in the study.  A photo of that coat of arms is below. In the frame was the following explanation, but with no citations. The information in the second paragraph I believe is more important to my specific branch of the family, although I am happy to be proved wrong.

Name in Gaelic: Mac Amhalghaidh (Son of Amhalghaidh, an ancient Irish personal name) Mac Amhlaoibh (Son of Amnloaibh or Olaf)

McCauley, a surname of great antiquity, is borne by the descendants of several distinct Irish families.  In medieval Ireland, the most prominent was the Mac Amhalghaidt sept. Established in County Westmeath.  Of royal lineage, they stemmed from Niall of the nine hostage, king of Ireland 379 to 406.  Their name was taken from Auley, Niall’s direct descendent who flourished in the 1200’s.  Lords of Calraighe, the McCauley Chiefs were seated at Ballylougnoe, possessing a vast territory, known as McCauley’s Country” in the Elizabethan Faints.  It comprised a sizeable portion of Westmeath and the adjacent areas of County Offaly.

In the north of Ireland, where the majority of the surname reside, McCauleys have a different Ancestry.  One sept, Mac Amhlaoidh in Gaelic, were a branch of the Maguires.  Auley from whom they derived their surnames, was a son of Domm Carrach, the first Maguire Monarch of Fermanagh who died in the year 1302.  It is believed that this Auley and his sons first crossed the river Ernie, gaining control of south Fermanagh for the Maguires.  The predominance of the sept in this region is preserved in the barony of Clanawley.

Some of the name in Ulster are of Scottish stock. Stemming from the Clan Mac Leod or Clan Alpin. The former, Mac Amhlaibh (pronounced Auley in Gaelic) are from Lewis in the Hebrides, claiming as their forebear, Olave the Black, brother of Magnus, last king of Man and the Isles.  The McCauleys of the Clan Alpin origin was seated at Ardincape, Dunbartonshire, (Loch Lomond Scotland). They came to Ireland in the 16^th century with the Mc Donnell’s as gallowglasses (mercenary soldiers), setting in the Glens of Antrim.