Why So Many Irish Last Names Start With O’ or Mc Why do so many Irish surnames start with O’ or Mc? These ancient Gaelic prefixes reveal your clan, lineage, and medieval ancestry. If your last name begins with O’ or Mac, you’re carrying a linguistic link to Ireland’s past. Drop your surname in the comments 👇 Irish last names Irish surnames O and Mc Irish names Gaelic surnames Irish ancestry Irish family names Irish clan names O prefix meaning Mac prefix meaning Irish genealogy Irish heritage Ga