"Scot-Irish" or "Scotch-Irish" are "Americanisms." Meaning, that is the only place in the world that we are known by that tag. The rest of the world will refer to us as Ulster Scots.
The term has come into existance to describe those peoples...and descendants there of.... who were sent from Scotland to Ireland by the English king to hold the Plantations. The families were mostly Lowland Scots from border area and a bit north, but not the Highand area. Lowland Scots, generally are more in the category of Noble Families than Clans... although there are clans in the lowlands... but that is a topic for another discussion.
The Ulster Scots settled and managed the Plantations for a couple of hundred years and did not tend to intermarry with the Irish. They maintained their Scottish identity. And the Irish may not have received them too kindly as they were "invaders" after a fashion. Intermarrying seemingly was not desired by either party and each kept to their own.
The confusion comes in when they began to immigrate to America.
The immigrants clearly had just gotten off a boat from Ireland. Their families had lived in Ireland for 100 years or more. And yet, they maintained, insisted, they were Scottish and not Irish. In the course of 100 years of immigration from the Plantations, they began to be known in
America as "Scots-Irish" or "Scotch-Irish". It was not a term immediately attributed to them.
And to this day, Americans of this descent will have their preference. "Scotch" as a descriptor of someone of Scottish descent is not accepted by most of Scottish descent, as it is something the English called us. Scotch is something one drinks. "Scots" is the preferred descriptor. Some people carry this over to the "Scots/Scotch-Irish" term. However, in this useage, "Scotch-Irish" is equally appropriate and acceptable as "Scots-Irish."
The American Heritage Dictionary provides the following definition:
Scotch-IÂ·rish n. 1. The people of Scotland who settled in northern Ireland or their descendants, especially those who emigrated to America. adj. 1. Of or relating to the Scotch-Irish.
The typical immigration pattern is from Ulster to Pennsylvania and from there spreading to the Appalachias and beyond.
Timing is 1700-1800s.
You have already been given Lyman as a resource. You will also want to explore Hanna's research.
Lauren M. Boyd, FSA Scot
Scottish Information Society
A Scot-Irish Descendant