I have a two map distributuons of the Gray surname. Grenham identifies the Gray surname as mainly of Scots origin, but also Native Irish derived from Mac Cathail Riabhaigh. McLysaght makes a distinction between English and Scots. The first map breaks down the 1901 census by religious affiliation. A clear divide can be seen between the Grays to the south who are Roman Catholic and the Ulster based Grays who are largely Presbyterian.
A Researcher searching for the Scots Irish origin for the Millikens. The Ulster Muster Roll (circa references Millikin in the Baronies of “Clougher” and “ Tome”. The 1901 Census finds Millikens and Millikins in the modern barony of Upper Toome.