John Rosbrugh was born in Enniskillen, County Fermanagh, Northern Ireland. He to the United States along with his older brother, William. The family was originally from Craigie, County Ayrshire, Scotland. His ancestors went to Ireland during the settling of the Ulster Plantation. In 1733 his young wife Sarah died in childbirth along with their only child. He was a tradesman but well enough educated to prepare himself for college.