1.  Jordan R. Dodd, ed.  1993.  Virginia Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):

Mcdowell, William

Thompson, Agnes

Nov 12, 1802

Monroe Co.

2a.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313).  Please see my WARNING regarding use of this database (the numerical data have the genders switched).  Granted, in this case the switch doesn't matter, but I like to draw attention to the problem whenever the opportunity arises. 

1810

McDowel, William

KY

Christian Co.

p. 76

20010-2001000

2b.  1810 Census Index/Images (online at Ancestry.com; Image #24 of 66; extracted by Diana Gale Matthiesen):

1810

KY

Christian Co.

Hopkinsville

p. 76/553

Ln. 7

William McDowel

20010-20010-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	9 or under	1800-1810	= Son B = Son A
1 male	26-44	1765-1784	= William
2 females	9 or under	1800-1810	= Daughter B = Daughter A
1 female	26-44	1765-1784	= Agnes

3.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  this is the closest I could come; it may not be our subject, but he does appear to be a city-dweller, which makes him more mobile than a farmer.

1820

McDowell, William

KY

Logan Co.

Russelville

p. 36

4.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):  again, no assurances this is our subject, and subject's children are now old enough to be appearing in the censuses.

1830

McDowell, William

KY

Todd Co.

p. 371

5.  Census Index:  U.S. Selected Counties, 1840 (Broderbund CD-316):  ditto.

1840

McDowell, William

KY

Todd Co.

Todd City

p. 261

6.  Census Index:  U.S. Selected Counties, 1850 (Broderbund CD-317):  not our subject (William is age 48, has wife Sarah).  Really wouldn't expect our subject to still be living.

1850

McDouel, William

KY

Logan Co.

District 2

p. 128

7.  A.B. Willhite.  [n.d.]  Christian Co., Kentucky, Tax List, 1804-1809.  (self-published; available from author at 4396 Coopertown Rd., Russellville, KY 42276, or from the Christian County Genealogical Society, Hopkinsville, KY):

Pg. in Willhite	Year	Dist.*	Last Name	First Name	A	B	C	D	E	Acres	Watercourse
	1804		[not found]
	1805		[not found]
60	1806	North	McDowel	Wm	1				3	69  21	T W T W
127	1807	East	McDowel	Wm	1	1			2	200  50	E F Whipporwill
171	1808	East	McDowel	Wm	1				3	245	E F
220	1809	East	McDowal	Wm	1				4	245	E F
Legend for numerical data: A = White Males 21 or over; B = White Males 16-20 (this column not used in 1809); C = Blacks over 16; D = Total Blacks; E = Horses
Abbreviations:  T W = Tradewater River; E F = Elk Fork of the Red River
*The county was divided into just two districts:  from 1804 to 1806, into North and South Districts; and from 1807 to 1809, into East and West Districts.

I wonder if the William on the Tradewater is really the same person as the one on the Elk Fork?  The Elk Fork is flows southward in central and eastern Todd Co., then joins the Red River in Tennessee.  Whipporwill Creek is also a tributary of the Red River.  It flows southeastwards out of central Todd Co. into Logan Co. before joining the Red River in Tennessee.  In central Todd Co., the two tributaries are very near each other, which may explain why it appears the "Whipporwill Creek" land was at times lumped with the Elk Fork land.

8.  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
372	McDowell, Wm	245	11	365	10-5-1803	Christian	Elk Fk Red R