A first thing to consider is that Union County was not formed until 1842 from parts of Anson and Mecklenberg and in turn those counties were formed from others (parts of this going back to Bath County in 1696). I would first try to ascertain which part of Union County in which you know he lived or died, then work backward in time with appropriate county names and see what records can be found. Finding where certain former county records reside can be a bit of a challenge and places like Ancestry don't always have the digitized records properly indexed. If the first marriage is documented as Mecklenberg County, that may be a clue -- it may be he never moved, just the county boundaries moved.
