Paul, I am hoping that you are still working on this Briggs line as I am working on the presumption that my Briggs line ties in to this John Briggs of yours.
My Elias Briggs, b.c. 1798 VA(marr. 1823 in Scott Co. IN, dying in Schuyler Co. IL in 1856) MAY have been the son of the Isaac Briggs, b.c. 1762 in PA(Cumberland or Westmoreland Co., can't tell for sure which yet)and who was married to a Mary Murphy and by 1820 was living in Ohio/Marshall counties VA/W.VA.Don't have the absolute proof yet of Elias's connection to Isaac, but there is some census info,etc., which seems to make this connection likely.
If you have any details on the John Briggs who was in Westmoreland co. PA, I would appreciate hearing from you. Thanks and best regards, Larry D.H. Coats