MacQuillan is a surname of Irish origin, primarily associated with the province of Ulster. It is derived from the Gaelic name Mac Cuillinn, meaning "son of Cuillin." The name is linked to several historical figures and families in Ireland, particularly in County Antrim. The MacQuillans were known as a prominent clan in medieval Ireland, often involved in local governance and land ownership. They played a significant role in the region's history, particularly during the Tudor conquest of Ireland. Today, the name can be found among descendants in various parts of the world, especially in North America.