Greetings To All My Kilted Brethren!

I have recently discovered--thanks largely to Ancestry.com--a tantalizing amount of information about my matrilineal great-great grandfather Alford Dyer who, at various times, served as Sheriff, County Clerk, Schoolmaster, and I think also Deeds Recorder or some other such elected/appointed post, of Trigg County in the southwest part of the US state of Kentucky. As an African-American of mixed race descent, this bit of British provenance is a source of both extreme pride and curiosity for me, but my burning question about him is...was he Scottish, Irish, English, or Welsh? The trickiness of the surname Dyer of course is that it can be either an English occupational name, or, ironically enough in my case, the English variant spelling of Dwyer (Duibhir). I will likely need to hire a professional geneologist to get a definitive answer, but for the moment I can only speculate as to whether he arrived in the US as part of the 1840s post-famine Great Migration, or if he was descended from forebears who came to the US before then (perhaps originally landing in Virginia).

I am aware that the American states of Kentucky and Tennessee were overwhelmingly settled by Scots-Irish, so my guess that he was not English or Welsh is a fairly educated one, but it's still just a guess. I am wondering if anyone else with ancestry from these states have uncovered any data as to exactly how predominant they were?