He is descended from several Dutch families that came to America when New York was a Colony of the Netherlands.
His paternal immigrant ancestor Christian Barentsen van Hoorn had a house lot at Wall Street and Broadway which is now part of Trinity Churchyard, and was Fire Marshal of Manhattan in the 1650s before moving to the area of Wilmington, Delaware.
His grandmother, Alice Sleght Van Horn, may have been descended from Catherine Trico Rapalgie, one of whose daughters was reputed to be the first white child born in New Netherland.
Immediately following his term in the Pennsylvania House, he was elected as a Republican or Jeffersonian, to the Seventh and Eighth United States Congresses.
Dorothy had 11 more children with Isaac: Van Horne died February 2, 1834, in Zanesville, Ohio.