He served during the Revolutionary War as a member of the Dutchess County Militia, Colonel Field's 3rd NY Regiment. The US Census of 1790 shows Jonah Barnum, with two free white males under 16 and six free white females, living in Southeast, Dutchess County, New York.
In Putnam County, a little west of the De Forest Corners intersection, on Putnam Lake Road, is a bridge. Immediately west of the bridge, on the north side of the road, is a private lane which leads 250 feet north to the old Barnum Family Cemetery.