Still having trouble finding where that Virginian was from in Virginia after they moved. If you have a Virginia Revolutionary War ancestor then it might be easier to locate them than you think. Knowing the name of the company captain will go a long way in helping you. If the service was in the Continental Line and you know the name of the captain then consult E. M. Sanchez-Saavedra's A Guide to Virginia Military Organizations in the American Revolution, 1774 - 1787. In many instances the entry might look something like this:
3rd Virginia Regiment of Foot
Captain Charles West
Raised in Loudoun.
Loudoun at the time of the Revolution was the most populous county, they even had a draft riot.
Of course, if you are interested in the 3rd Virginia, Joan Peters has just authored a two volume set on the unit. The Third Virginia Regiment of the Foot, 1776 - 1778, With Flags Flying and Drums Beating. The first volume is a history of the unit and the second volume are the biographies of the soldiers.
If your soldier was in the militia and you know one of the officers then J. T. McAllister's Virginia Militia in the Revolutionary War is the best way to determine what county that officer was from, through his militia appointment.
A typical entry might look like this:
Section 261 - Fauquier
Atwell, Francis, gent., Cp., Sept. 28, 1778
If it turns out you have an interest in Fauquier then T. Triplett Russell and John K. Gott's Fauquier County in the Revolution contains a listing of soldiers from the county along with the history of the county's participation in the war.
So it is possible if you know an officer in the company that your ancestor served in you can find the county that the soldier lived in.