For all those McCains with Hamilton connections; there is some very good research on going about Hance Hamilton who was the de facto leader of the Marsh Creek Settlement in the 1700s. There are several McCain Hamilton marriages, both in the Colonies and in Ireland, and there was a very consistent and strong bond between these two families.
The new research as peeled away some pseudo history concerning Hance Hamilton. For example, it is often stated his father was a Hance Hamilton Sr who led 140 families to the Colonies in 1729, yet there are no known records that support this. To date, no records have been located that even suggest Hance Hamilton's father was named Hance. A group of 140 families would have needed several large ships at the very least and there is no records in the Colonies nor Ireland of this event. On the other hand, there are records of Hamiltons coming over in 1729 on a smaller ship and landing at New Castle, Delaware. Hance could have been aboard this smaller ship, we do not know for certain, but we do know just a few years later he shows up in the Marsh Creek Settlement, fully grown, very active, and a leader of men.
The early life and parents of Hance Hamilton are for the time being a mystery. There is now some DNA results that connect Hance to the Abercorn Hamiltons in east Donegal and northwest Tyrone. Of interest, some of our McCains were living on the Abercorn Hamilton lands prior to coming the Colonies and the McCain Hamilton marriages in Ireland are with the Abercorn line. Given this information, it does look like Hance Hamilton is connected to that particular Hamilton line. If so, it is very likely that eventually records of his family will turn up in Ireland.
Part of the confusion with Hance comes from the birth year listed on his stone in Gettysburg, which is 1721. The stone that exist today is not the original one. It was replaced in the late 1800s as the original stone was badly weathered and broken. Given the age of his oldest son it is very probable that the 1721 date is an error. He would be older, so perhaps the original stone read 1711 or some other date that was illegible by the late 1800s.