The question here is, was B.B. KING correct about his birthplace, as given in his bio?  If he was born in Madison County and his father moved to Lincoln County in 1847, why do we not find William in the 1840 census of Madison County?

1a.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org). 

William KING Spouse: Anna BAKER Marriage: 08 Sep 1829, Madison, Kentucky Source: patron submission

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

King, William	Mcclain, Peggy	17 Sep 1800	Lincoln Co.
King, William	Jarvis, Sally	02 Nov 1802	Madison Co.
King, William	Conner, Rebecca	20 May 1820	Madison Co.
King, William	Clinton, Elizabeth	05 Nov 1839	Garrard Co.

These are the only William KING marriages in Garrard, Lincoln, or Madison Co., KY, on this CD.

1c.  Marriage Index:  Kentucky, 1851-1900.  Liahona Research, Orem, UT (Broderbund CD-233):

King, Nancy

Helton, Arnold

4 Nov 1851

Lincoln Co.

2.  1810 Census Index/Images (online at Ancestry.com; Image #10 of 12; extracted by Diana Gale Matthiesen):

1810

KY

Madison Co.

Roll M252_7

p. 242/854

Ln. 14

William King

10010-30010-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1800-1810	= Son A
1 male	26-44	1765-1784	= William (b. 1783)
3 females	9 or under	1800-1810	= Daughter C = Daughter B = Daughter A
1 female	26-44	1765-1784	= Wife-1

This William KING is the only one indexed Madison Co., KY (I also did a page-by-page check of the county); there were none indexed in Lincoln or Garrard Cos.  Other KINGs in Madison County were Aaron, Joel, and Michael.  This William KING appears to be the one who married Sally JARVIS, who — based on a file at WorldConnect — was the son of Aaron KING & Hannah DYER and the brother of Joel KING.  While the Madison County census list was roughly alphabetized, we find Aaron and Joel on adjacent lines and William just one line away, while Michael is on another page.  So, if our subject's father is in the county, he was either missed by the enumerator or is unmarried (not head-of-household) and is living in some other household.

3.  1830

4.  1840

5.  1850 Census Index/Images (online at Ancestry.com; Image #22 of 91):  District No. 2, Lincoln Co., KY, p. 287B, 156/156, enumerated 1 Aug 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen): 

Wm King	50	M		Laborer		Va
Annie King	40	F				"
Chas King	14	M				"
Benj King	10	M				"
George King	8	M				"
Wm King	6	M				"
Nancy King	20	F				"
Rhoda King	17	F				"
Mary King	10	F				"

These birthdates for the parents are reasonable if the year given for their marriage (viz., 1829) is correct, though Annie may be 45, not 40 (see 1860).  However, if William's father was born in 1783, as said in son Benjamin's bio, then it's unlikely William was born as early as 1800.  Annie and the children were born in Kentucky, not Virginia.  The children are out of sequence because this enumerator placed male children before female children.

6.  1860 Census Index/Images (online at Ancestry.com, Image #68 of 181):  Stanford, Lincoln Co., KY, p. 68, PN 68, 437/437, enumerated 19 Jul 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen): 

Wm King	83	M		Laborer			Va
Anna  "	55	F					Ky
Charles "	25	M					"
George  "	16	M					"

Anna's age is still reasonable, but William's is not, unless our subject has died and Widow Anna is living with her widowed father-in-law, which is certainly possible.

.  1860 Census Index/Images (online at Genealogy.com, Image #3 of 8):  Stanford P.O., Stanford, Lincoln Co., KY, Roll 382 (Book 1), p. 3, PN 3, 16/16, enumerated 7 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen): 

Peter Straub	34	M		Master Tinner	800	800	Switzerland
Mary    "	20	F					Kentucky
[Peter & Mary's children]
Riley King	15	M		Apprentice Tinner			"
A R Pe??y	22	M		Druggist			Ohio

3.  1870 Census Index/Images (online at Genealogy.com, Image #14 of 20):  Stanford P.O., Town of Stanford, Lincoln Co., KY, Roll 482 (Book 1), p. 118B, PN 4, 26/26, enumerated 1 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

Straub Peter	48	M	W	Tinner			Switzerland
______ Mary	32	F	W	Keeping house			Kentucky
[Peter & Mary's children]
King Annie	60	F	W		600		Indiana

4.  1880 Census Index/Images (online at Ancestry.com):  not found — at least, there was no Ann/Anna/Annie KING in Kentucky over the age of 55, much less 70.

5.  Charles Kerr, ed.  1922.  History of Kentucky.  5 vols.  American Historical Society, Chicago and New York (online at Ancestry.com).  Except from a biographical sketch of our subjects' son, Benjamin Burke ["B.B.] KING, in Vol. 5, on p. 205.  For the full excerpt, see B.B.'s family group sheet.

B. B. KING... was born in Madison County, Kentucky, January 29, 1839.  His grandfather, John Louis King, came from Ireland and spent the rest of his life as a Virginia planter.  He married Nancy Jane Pence, a native of Holland.  Their son, William King, was born in Virginia in 1783, soon after the close of the Revolutionary war.  He lived in his native state until he was twenty-six, and in 1809 identified himself with the pioneer district of Kentucky in Madison County, where he married and where he followed his trade as a cooper and also farmed.  For four years he had his home and work at Indianapolis, Indiana, then returned to Madison County, also lived in Garrard County, and from 1847 until his death in 1863 lived on and operated a farm in Lincoln County.  He was an old-line whig in politics.  William King married Annie Baker, who was born in Madison County, Kentucky, in 1790, and died at Stanford in Lincoln County.  They became the parents of seven children:  Nancy Jane was the wife of Arnold Hilton, a farmer, and both died in Lincoln County; Rhoda Ellen had two husbands, Richard Whittaker and John Gray, the first a shoemaker and the latter a farmer, and all are now deceased; Charles Alfred was a Lincoln County farmer; Mary, living at Stanford, is the widow of Peter Straub, a coppersmith; B. B. King is the fifth in the family; George Washington died while a Union soldier in the Civil war; and William Riley is a retired tinner and coppersmith, and living at Moreland... On September 1, 1864, at Stanford, Kentucky, Mr. [B.B.] King married Miss Lizzie Berry, daughter of Mr. and Mrs. W.B. Berry...

If "B.B." (Benjamin Burke) was born in 1839, his mother was certainly not born in 1790 — it's just not possible biologically.

.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).  Gives father of Benjamin Burke KING as the William KING who married Annie BAKER, but shows this William's father to be another William KING, one who married Elizabeth WELLS, and then this elder William as the son of John Louis KING.  There is a William KING with wife, Elizabeth, and son, Benjamin, in the