Do the Scotch-Irish get their own category or are they parceled out in some manner?
They do get their own category. I used Statistical Atlas' website, I just hadn't gotten to making that list yet. Here is the top ten:
1. North Carolin: 4.30%
2. South Carolina: 3.83%
3. Tennessee: 3.19%
4. Mississippi: 2.77%
5. Virginia: 2.67%
6. Alabama: 2.38%
7. Texas: 2.37%
8. Georgia: 2.31%
9. New Mexico: 2.28% (very surprised by this)
10. West Virginia: 2.25%
I don't know why. Eastern New Mexico is basically indistinguishable from the Texas Panhandle - culturally, politically and demographically.
It appears that the assumption that persons who are of Hispanic ancestry can not be of Scotch-Ancestry is erroneous.
The top county in Texas is Zapata, while in New Mexico it is Rio Arriba, Catron, and Los Alamo. There may be a disproportional share of nuclear physicists who are Scotch-Irish.
