pmorgan53 on Family Tree Circles

Despite my father's 25 years of research, we've many genealogical mysteries yet to solve -- but where we're really stuck is before 1800, when my fourth great-grandfather, John Morgan, lived in Frederick County, VA. He married Elizabeth Gant/Gaunt in 1804 and their progeny included Col. Benjamin Morgan. Over the years, Frederick County was subdivided into smaller counties and by 1836, all of the Morgans appear to have ended up in that portion that became Clarke County. It was still called Frederick when John Morgan died in 1832, but his will leaves us clueless. Further, his gravestone was buried up to its ears when it was moved from the family graveyard at Benjamin's home called "Hill & Dale," so we can't make out the birth date, though we believe it's between 1771-1778. How can we find this information with such a common name? We're stuck, unable to verify his birth date or location, his parents, or any siblings. Can anyone advise?