The name “McCullough” is a Celtic name that may have derived from the Scottish name McCulloch but were interpreted from a local Ulster context. However, it is possible that the McCullough name has multiple orgins, some of which may have derived independently. It is often said that the Irish spelling “McCullough” derives from the Irish Gaelic “mac Con Uladh” or “mac cu Uladh”, meaning “son of the hound of Ulster.” This patronym may pay homage to the legendary Cu Chulainn of the Ulster Cycle of Irish Mythology.
In Scotland, the name McCulloch is “Ultra memoriam hominium,” or from before human memory. According to SurnameDB: “The first known recording is that of Thomas Maculagh, given in the records of the proceedings of the government of Scotland as being “del counte de Wyggetone” in the year 1296. This was when he gave his allegiance to the government of John Balioll known as “The Interregnum” of 1296, it being overthrown by Robert, The Bruce, in 1306.”