The Milltown Heritage Society covers the history of Liskeevy Parish. They are an award-winning heritage society. On their website, it says that the O Donovan Field names have a Mr J Griffin as the landowner in 1838.
I looked in the wills and found a John Griffin Gentleman Tuam leaving his estate to a John Griffin Gentleman Dublin. I attach what I found. I do not know if it is the same person.