1.  Marriage Record:

2.  Colonial Census

3.  1790

4.  1800

5.  1810 Census (extracted by A. Robert Matthiesen, see 1810 Table): 

1810

Robert Thompson

KY

Christian Co.

p. 115

00001-10111-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	45 or over	in or bef. 1765	= Robert Sr. (b. ca. 1740)
1 female	9 or under	1800-1810	= ?
1 female	16-25	1784-1794	= Daughter B
1 female	26-44	1765-1784	= Daughter A
1 female	45 or over	in or bef. 1765	= Agnes

Agnes could only be the mother of the youngest girl if she is just 45 and the girl is an infant or toddler.  More likely, a young child in the home of an older couple is a grandchild.  Many scenarios could be imagined, but I think it highly unlikely she is their daughter.

6.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  not found.  Robert obviously died before 1820 because there is a squabble in the courts over his estate in 1818.  Agnes is not a party to the squabble, so she must have pre-deceased Robert.

7.  Willard Rouse Jillson.  1925.  The Kentucky Land Grants. Filson Club Publ., Louisville, KY (online at Ancestry.com; Broderbund CD-650):

Part 1, Chap. IV, Grants South of Green River, 1797-1866
Pg	Grantee	Acres	Book	Pg	Date	County	Watercourse
422	Thompson, Robt	200	10	29	3-8-1799	Logan	Elk Fk Red R

8.  Queries at Christian County, Kentucky, Message Boards (online at Ancestry.com):

Messages posted under the titles, "Thompson Family" and "Robert and Agnes Thompson of Christian Co."

Robert is said to have gone first to Rich Creek, Greenbrier Co., VA [now Monroe Co., WV], then to Christian [now Todd] Co., KY, ca. 1806, then to have left Christian Co. ca. 1810.

9.  James Taylor Killebrew.  1999.  County Court Order Book "C," Parts 1 & 2, Christian County, Kentucky, 1814-1819.  Christian County Genealogical Society (1101 Bethel St., Hopkinsville, KY 42240).  See son, Robert's page for the bruhaha over subject's estate. 

10.  WorldConnect (online at RootsWeb.com).

11.  Emails from Robert E. Graham.