Martin: I read your comments and took a look in the IGI for more information.John Briggs Jr more likely born between 1775 and 1779 based on his siblings births. Joseph born 1770 Wrightstown, PA Frances born 19 Oct 1773, Bucks Co Martha born 25 June 1780, Newtown, PA Mahlon born abt 1790, Newtown, PA
You probably already have the information, but John Briggs SR, born 9 December 1742 in Middletown, PA, the son of John Briggs and Mary Watson,married Letitia Buckman in 1769 in Bucks Co., PA.
I could not find a marriage for John Briggs to Mary Vandegrift, so I searched on her name.IGI not very clear on her as it shows her parents as Jacob Vandegrift and Catherine Hufte and that she was born about 1759 in Bensalem Township, PA - later married to ? Bennett about 1796OR Mary Vandegrift born 1788 in Bensalem, same parents, married in 1810 to John Bronaux.There was No listing in the IGI for a John Bronaux, and that name is a far cry from Briggs, but I have seen stranger.I could find no entries for the birth of either Jacob or Benjamin.