15+ years! - So I'm not holding out a lot of hope here. I have two James Allisons from Donegal in my ancestry, but neither is your ancestor James. Just hoping you have more about the Donegal Allisons and maybe could shed some light.
The first James was born before 1820 (likely by a good number of years) in Donegal. He married Nancy Somers (some claim it's Sawyers). Both likely died in Donegal, but I have no documentation of their deaths.
Their son, James M. Allison, b. 18 Nov 1835 in Donegal, d. 6 Apr 1916 in Menard County, Illinois. His wife was Ann (or Anne) Montgomery, b. 4 Apr 1835 in Donegal. d. 18 Oct 1906 in Logan County, Illinois.
Do those names ring any bells? I have no parents for Ann Montgomery, or for the elder James and his wife Nancy.