Hi Fred, I don't know if you are still wondering about this question, but I'll add my two cents anyway. I am a little bit familiar with the St Regis Mohawk community, or, it is more commonly known today, Akwesasne. The territory existed along the St Lawrence River before any boundary was drawn between the US and Canada, or between Quebec and Ontario, and today, different parts of the Akwesasne territory overlap with all three of these entities (New York, Ontario, and Quebec). This makes historical research tricky!
However, I think I can help with the mention of "Island" -- I would guess that this refers to Cornwall Island, which is a large island in the St. Lawrence River that is part of Akwesasne territory. Or maybe to one of the smaller islands in the river -- there are many. However, I have heard people relatively recently refer to Cornwall Island as just "the Island." Technically, Cornwall Island overlaps with Ontario, while most of the rest of the Akwesasne islands are classified as Quebec, but as I said, everything is very close together.
Good luck!