Fiants
In the Elizabethan Fiants (1554–1601) there are no less than 51 persons of the name mentioned, spelled in 12 variant forms (usually MacUlick, MacUllock, etc.). The majority of these are in Connacht, mainly co. Galway, and they frequently appear in association with Burkes, as also do quite a number in Munster. There were no (Mc)Gillicks at that time in the Cavan-Meath area. And none are listed as being there in the 1659 census (but Cavan is missing from it). There is only one entry for the name in the Fiants of Henry VIII to Mary: one James Willock, a kern (lightly armed fighting man) of Ballybretnagh, Co. Westmeath.
It was the opinion of the late Dr. Edward MacLysaght, first Chief Herald of Ireland, that the surname (Mc)Gillick was likely taken to the adjoining counties of Cavan and Meath by migrating kerns of that name, who began families which, in due course, multiplied and originated the considerable number of persons found there in the 1800s.
Read more about this topic: Gillick (surname)