Samuel Smitheman (Smitherman) was first found in "Loudoun County , Virginia Tithables 1757-1786" by Marty Hiatt & Craig Roberts Scott.  Also copied from books by Ruth and Sam Sparacio (three volumes, tithable lists for Loudoun County 1758-1781).  He is then found in Fairfax County, Virigina.

On July 10, 1784 Samuel Smitherman and William Fitzhugh Jr entered into an agreement in which Samuel would purchase 134 1/2 acres of land along the Pohick Creek in the Southeastern area of Fairfax County, Virginia. Also listed in the Deed were Sarah, his second wife and Hugh, his youngest son.

In the Fairfax County, Virginia Court Order Book 1789-91, Part 1, September 23, 1789, page 33.  Samuel Smitherman is listed as a tithable with land near the road from Hallace’s old field to where it intersects the Pohick road by John Fowler’s Plantation.

Again in the COB 1789-91, 18 July, 1791, page 252  Samuel is listed as a tithable with land on the road, from the Turnpike road, at Hollis’s to where it Intersects the Pohick road at Jn Fowlers fence.

And then in the Fairfax County Minute Book 1797-98, 16 October 1797, page 123 a Samuel Smitherman and Sons was alloted an overseer for the road from the Turnpike road at Hollices old field to where it intersects the Pohick road at John Fowlers plantation.

It is believed that Samuel Smytheman, the immigrant died sometime around 1790.  So it's possible the Samuel listed in the Court Order Books is his son Samuel.  

If you would like to read more about the Fairfax County Road Orders, download this pdf file

Take a look the Fairfax County, Virginia Historical Map, in the areas C-3 and C-4.  I believe this is the area in which Samuel and his family lived and are most likely buried.  I derived this from reading the Fairfax County Road Orders and by using the information in the Fairfax County Historical Maps w/ features on land grand surveys.