I do believe that this John McCartney may be in my line of McCartys as Bill Davidson suggested. There are no McCartneys in VA shown in either the 1790 or 1800 census. There are quite a few in PA: 20 in 1790 and 24 in 1800. At this time what is now western PA was claimed by both PA and VA. At one point each state laid out counties in this area.
"My" Joseph McCarty was in Washington County, PA, for the 1810 census, and in Rockbridge County, VA, for the 1820 census. A biog of Joseph's son John describes this migration. The 1790 census shows three McCartneys in Washington County, PA,: James, John, and John Jr. Both of these Johns are missing from the 1800 census. Perhaps one of these is the Jno McCartney of Botetourt County, VA.
Anyone have any ideas as to how to prove this?