First found in Argyllshire, where they were seated at Brae Lochaber from ancient times being descended from an ancient chieftain of the MacDonnells of Keppoch who were, in turn, descended from the Lords of the Isles. It has been suggested that the MacKillops or MacGilps may be the sons of Ilpin or Gilpin, in Iam Lom's "Soiidh do'n Ghreumach.".

Descendents of Dalriadan-Scottish families still populate many communities across North America. They are particularly common in Canada, since many went north as United Empire Loyalists at the time of the American War of Independence. Much later, in the late 19th and early 20th centuries, the highland games and clan societies that now dot North America sprang up, allowing many Scots to recover their lost national heritage. Some of the first immigrants to cross the Atlantic and come to North America bore the name McKillop, or a variant listed above: John McKillop arrived in Boston Mass in 1767; Hugh McKillop arrived in Pennsylvania in 1833; Robert McKillup arrived in Pennsylvania in 1839.

For more information on the last name McKillop, the PDF Surname History is available for purchase as well as other products.