That should be Order Book D page 106, not Will Book.
A James Williamson first appears in the Index to the 1758-1781 Loudoun Co Tithables by the Sparacios in 1760 and last appears in 1779. Except for the following years, he is the only taxable person listed in his household.
Williamson, James; Dallis, James - 2 tithables; 10 squirrel scalps, List taken for Shelburn Parish by Geo. West 1771 Williamson, James; Williamson, Henry - 2 tithables, List taken by George West 1772 Williamson, James; Williamson, Henry - 2 tithables, List taken by Geo. West 1773 Williamson, James; Williamson, Henry - 2 tithables, List taken by G. West for Shelburne Parish for 1774
There is also a James Williamson who appears on the 1783 Loudoun Co Personal Property Tax Lists.
From “Index to Loudoun Co Deed Books A-Z, 1757-1800” by Pat Duncan:
Bk:Pg: I:413Date: 11 Oct 1773Returned to court: 11 Oct 1773 Gent. Lewis ELLZEY of Ffx to planter James WILLIAMSON (wife Mary) of Ldn. Lease for lives of 150ac on Goose Creek. Wit: Solomon HARDY, Hy. POTTEN.
Bk:Pg: O:131Date: 31 Jul 1784Returned to court: 11 Oct 1784 James WILLIAMSON & wife Mary of Ldn to Jacob YANDES of Ldn. Assignment of lease of 150ac. Wit: Francis SANDERS, Richard PRICE, John PRICE.