Re: curious American
I think that I have what you are looking for.
The map that you saw might have been from one of three books by Dr. Edward MacLysaght. In his books, "Irish Families," "More Irish Families," and "The Surnames of Ireland," MacLysaght has provided maps showing locationsof both the Gaelic Septs, and some Hiberno-Norman families.
MacLysaght states that the O'Loans are the O Luain, and that their principle sept is of Oriel. On his map, he shows the OLoan to be on the western section of the border between Counties Monaghan and Tyrone.
MacLysaght's books are still available. I found my copies at Amazon.com.
Mary (McClendon) Becker
Oriel Septs of Ireland DNA Project