"The Book of Ulster Surnames" by Robert Bell -- "MacCullough (also Cully, MacCullagh and MacCully) Taken together the origins of these native Ulster and Scottish Planter names are a little complicated. MacCullough and MacCullagh together constitute one of the fifty most common names in Ulster and 80 per cent of those names in Ireland are of that provence. The names are most numerous in counties Antrim, Tyronne, and Down.
The Ulster Galic names Mac Cu' Uladh or Mac Con Uladh, both meaning 'son of the hound of Ulster', were anglicised as MacCullagh. (The name also gave rise to Coloe, Coloo, MacAnaul, MacAnulla, MacNaul and MacNully, but see also MacNally.) In Petty's 'census' of 1659 MacCullough was listed as one of the 'principal Irish names' in the Co. Antrim baronies of Antrim, Belfast, Carrickfergus and Toome and also in the barony of Lower Iveagh in Down. However, many of these must have been Scottish. By the mid-nineteenth century the name in Co. Antrim was concentrated in the east of the barony of Lower Antrim.
Many of the Ulster MacCulloughs stem originally from Scotland, where the name is spelt MacCulloch. These MacCulloughs can be of two origins. MacCulloch is and was common in the province of Galloway, whence stemmed so many of the Ulster settlers. Its origins, however, are totally obscure, and although it has been suggested that it derives from the Scots Gaelic Mac Cullaich, meaning 'son of the boar', it is possible that it too derives from MacCon Uladh and represents previous Irish settlers in Galloway.
Either way, it is known that it makes its first appearance in the Scottish records in 1296, when Thomas Maculagh del conte de Wiggetone (now Wigtown) rendered homage to Edward I. His family later held castles at Gatehouse of Fleet in Kirkcudbrightshir, and Creetown and Port William in Wigtownshire. It was in Galloway that the softened form MacCully arose, though it is also found in Tyrone as a variant of the Ulster name MacCullagh. (Cully as a native Ulster name can be derived from MacCullagh, especially in Tyronne, or from O'Cully, Gaelic O'Colla, a name from counties Armagh and Antrim.) Also in Wigtownshire, many of the Kellys and MacKellys changed their name to Maculloch (see Kelly).
Yet another connection of MacCulloughs, those of Oban in Argyllshire, belonged to Clan Dougall and were originally called MacLulich. This name, in Gaelic MacLulaich, meant 'son of Lulach' (an obsolet personnal name derived from the Old Gaelic lu and laogh, meaning 'little calf'). the progenitor of this family was MacCulloch Lulach, the son of Gillacomagan, Mormaer of Moray. MacCulloch Lulach became King of Scots when (notwithstanding Shakespeare's account) he succeeded MacBeth. Within a matter of months, however, he too was killed and was succeeded by Malcolm Canmore, c. 1157.
James MacCulloch of Wigtownshire was one of the fifty Scottish undertakers of the Ulster Plantation and in 1610 he was granted 1000 acres in Glenties in Donegal. Though he lost his grant four years later, he and his tenants remained.
In Ulster about one-third use the -agh ending and most of the remainder the -ough, although MacCullow and MacCulloch are also found. The -ough spelling is very much more common in counties Antrim and Down, but it must be remembered that the spellings do not necessarily denoted the origins of any particular family.
The Co. Donegal name MacColla (see Coll) has no connection with MacCullough or MacCullagh.
James Macullagh 1809-47, a brilliant mathematician and physicist, was born in Upper Badoney, Co. Tyrone. His suicide at the young age of 38 was thought to have been caused by a fit of madness brought on by overwork. John Edward MacCullagh, 1837-85, who became a famous actor in the USA, was born in Coleraine, Co. Derry."
"The Surnames of Scotland" by George Black -- "MacCulloch. - Much obscurity enshrouds the origin of this old Galwegian name, and no satisfactory pedigree of the family exists. They are said to be described in one of their charters as having their origin "ultra memoriam hominum." The name may be G. MacCullaich or MacC(h)ullach, "son of the boar.' The name first appears in 1296 when Thomas Maculagh del counte de Wyggetone rendered homage. His seal bears a squirrel and S'Thome Macculi (?). He appears again in the same year as a juror on inquest at Berwick along with his brother Michal and is probably the Thomas Makhulagh, sheriff of Wigtown, 1305. Michel Maculagh and William Maculaghe also rendered homage. Sir Patrick McCoulagh and Gilbert McCoulaghe were charter witnesses in Galloway, 1354. Sir Patrick Macologhe had an annuity of 100 marks "in recompense of his sufferings, and loss of his lands in Scotland for his allegiance" to the king of England 1360 and in 1363 as Sir Patrick M'Owlache had restoration of his lands.
(Black goes on to describe some other MacCulloughs/MacCullochs. Here are some of the spellings of the name he brings up) Patrick Makcowloch (1480), Patrick Mackullouch (1482), Symon McKowloch (1500), David M'Ulloch (1643), MacLulich, Makawllauch (1414), McCoulach (1410), M'Coulaghe (1352), M'Cowlach (1476), Makcowllach (1482), M'Cullauch (1439), Maccullo (1546), M'Cullogh (1685), M'Kowloche (1495), McColloch, McCullie, McCullo, McCulloh, McCully, McKeulloch, McKulloch, M'Alach, Mackculloch, Makculloch, M'Hulagh, M'Kulagh, and Malrcowlach (1444).