There has been so much controversy over who the Scotch-Irish are, or if the words should even be written differently, as in Scots-Irish. One of the best books ever written on this race, by Senator Jim Webb, uses Scots-Irish instead of the original Scotch-Irish, despite how thoroughly his research is in all other areas.
Though it is much ado about nothing, the proper or at least original term is in fact Scotch-Irish. Some would say that the term originated in America to differentiate Scottish-blooded settlers of Ireland from the later arriving Irish, and others say it only refers to those Scots settling in Ireland after or during the Plantation of Ulster, beginning about 1607 – folks coming principally from the lowlands.
However, the truth is that the term Scotch-Irish was used on April 14, 1573 in a manifesto issued by Queen Elizabeth concerning Scots already in Ireland for several generations. It is most likely that the term Scotch-Irish was a contraction of Scottish-Irish, which was meant to separate these people from the native Irish.
The contention that this race typically only included lowlanders is also easily dismissed, as probably half of all so-called Scotch-Irish surnames us the Mc prefix in front of them. Mc, which was originally the Gaelic "Mhic," was principally used in the Highlands and Islands of Scotland, from where many early Scots immigrated on their way to Northern Ireland (Ulster) and eventually on to America.
Since the earliest known form of the term was in fact "Scotch-Irish" and since it was used long before the Ulster Plantation, and long before immigration to America began, the most authentic acceptance of this race and its name is that of Scottish peoples settling in Northern Ireland from early times and being referred to as the Scottish-Irish, or the Scotch-Irish.
Some have taken exception to the word Scotch, because it also seems to apply to liquor, however, the true term is Scotch Whisky, just like Irish Whiskey (note the spelling difference between whisky in Scotland and whiskey in Ireland). If it was appropriate to randomly take the ch off Scotch and add an s to make it Scots, then it would be just as appropriate to take the sh off Irish, add an s and make it Iris. We would then be the Scots-Iris. All joking aside, the earliest, original term is my choice, and the long history of Mc families in Ireland before the plantation, specifically referred to as "Scotch-Irish" should eliminate the argument, but I suspect it will continue.