The surname McCulloch is rendered in several known spelling variations. Even members of the same family may see the accepted family spelling of their name change over the course of generations. This phenomenon is not unique to the McCulloch name. But one hypothesis for why the McCulloch name produced so many variations is because of the multicultural, multilingual nature of the British Isles and even Southwest Scotland. While the origins of the name name remain a mystery, the McCullochs were a family reportedly known since time immemorial in Galloway. We can speculate that the original name was from an “indigenous” Celtic people group such as Scots or Britons. (Well, as indigenous as anybody else). In reality, the adoption of a surname was a custom that started with the Normans. After the Normans (French speaking Norsemen) conquered England they advanced into and settle in Scotland as well. The McCullochs lived among the Norse-Gaelic tribes of Galloway. Those Norsemen adopted Gaelic culture, but still may have continued their own pronunciations and accents.
In the wars for Scottish Independence, the McCullochs paid homage to English King Edward I. It’s even been said that Patrick McCulloch of the early 14th century, a loyal supporter of John Balliol, had become “English.”
It should also be pointed out that Northern Ireland is only 12 miles away from Galloway by sea. The cultural exchange with Northern Ireland was likely to have been continuous. Fast forward to the Ulster Plantation, many Scots, including McCullochs, migrated to Northern Ireland. There McCullochs were greeted by existing populations of McCulloughs, who may or may not have been blood relatives.
So, the McCulloch name’s development may have had Celtic origins (Gaelic, Scot, or Briton), then was influenced by the pronunciations and interpretations of French Normans, Norse-Gaels, neighboring Gaels and Scots in Galloway, potentially Anglicized by English speakers, recorded by Latin scrivners, then eventually modernized by Northern Irish and North American kindred. With such a history, it’s no wonder a name could start like mac Ulagh or mac Cullach, then ultimately be rendered in modern times like McCulloch, McCullough, or even McCully.