I strongly suspect the Allison line was Scots-Irish. Through DNA testing we know we have Scottish roots and descended from the Clan Donald (McDonald). The name Allison probably evolved from McAllister, which was part of the Clan Donald. Allisons were early settlers of the Alamance community in Guilford County, North Carolina, which was largely Scots-Irish. The Alamance Presbyterian Church has Allisons as members and elders as early as 1764.
My Allison ancestors migrated from North Carolina to Georgia in early 1800s. From there some went to Alabama and others to South Carolina.
Highlighted names show the direct ancestor line of Guy C. Allison.