Must be the Virginia County Personal Property Tax Lists on microfilm at the Library of Virginia. They made a separate list of "Free Negroes and Mulattos" in 1833. They did the same in 1813 and most listed women as well that year. You can also find some years that they name children, occupations, and exact location in the county. I just added the Dinwiddie Tax Lists to my site, and they include separate lists for many years, but I stopped in 1819.
Paul
http://www.freeafricanamericans.com/Dinwiddie.htm