It is commonly accepted that the name McCullough derives from the Gaelic mac con Ulaidh, meaning “son of the hound of Ulster.” The name Mac Con Ulaidh was in use by 1532. According to the Annals of Loch Ce Seamus Mac Con Uladh or MacCullagh was killed at Dunbo (County Derry).

The spelling “McCullough” is simply one of the more common, modernized spellings of this Gaelic names. In addition to alternative spellings like McCollough, quite different iterations of the name like McInally and McNally may also derive from mac con Ulaidh.

It is interesting to note that the name Neely purportedly derives from “Mac Conghaile” and also means “son of the hound.”