John was born some six weeks before Valentine & Nancy were married.  So, was he Valentine's son from a prior marriage of his?  Or Nancy's son from a prior marriage or relationship of hers?  His descendants would be advised to do Y-DNA testing to at least determine whether or not he's really a SAMPSON.

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

Valentine SAMPSON Spouse: Nancy HIGGINS Marriage: 18 Jan 1821, Lawrence, Ohio Source: Marriage Records, 1817-1953, Lawrence County, Ohio. Probate Court.

Valentine SAMPSON Spouse: Catharine NEAL Marriage: 18 Jan 1846, Lawrence, Ohio Source: Marriage Records, 1817-1953, Lawrence County, Ohio. Probate Court.

2.  1830 Census Index/Images (online at Ancestry.com, Image #3 of 4; extracted by Diana Gale Matthiesen):

1830

OH

Lawrence Co.

Mason Twp.

Roll 134

p. 332

Ln. 25

Valentine Sampson

120 001 001 - 200 020

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	4 or under	1825-1830	= William (b. 1830)
2 males	5-9	1820-1825	= Son A = John (b. 1820)
1 male	30-39	1790-1800	= Valentine (b. 1798/9)
1 male	60-69	1760-1770	= Thomas SAMPSON?
2 females	4 or under	1825-1830	= Daughter B = Daughter A
2 females	20-29	1800-1810	= ? = Nancy (b. ca. 1802)

It is conceivable that the elder man is Valentine's widowed father, Thomas SAMPSON.  It is also conceivable that the elder man is David CORBIN, who married in 1828 in Lawrence Co., OH, to Elizabeth SAMPSON, probable sister of Valentine; I do not otherwise find David in the 1830 census.

3.  1840 Census Index/Images (online at Ancestry.com, Image #3 of 16; extracted by Diana Gale Matthiesen):

1840

OH

Lawrence Co.

Roll 407

pp. 47

Ln. 11

Valentine Sampson

011 200 100 - 212 001

0400000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	5-9	1830-1835	= George (b. 1831/2)
1 male	10-14	1825-1830	= William (b. 1830)
2 males	15-19	1820-1825	= Son A = John (b. 1820)
1 male	40-49	1790-1800	= Valentine (b. 1798/9)
2 females	4 or under	1835-1840	= Rebecca (b. 1837/8) = Nancy (b. 1835/6)
1 female	5-9	1830-1835	= Samantha (b. 1834/5)
2 females	10-14	1825-1830	= Daughter B = Daughter A
1 female	30-39	1800-1810	= Nancy (b. ca. 1802)
4	persons employed in agriculture

4.  1850 Census Every-Name-Index/Images (online at Ancestry.com, Image #10 of 27):  Mason Twp., Laurence [Lawrence] Co., OH, Roll M432_401, p. 359B, 63/63, enumerated 9 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

Valentine Sampson	51	M		Farmer	600	Va
William Sampson	19	M				Ohio
George Sampson	17	M				Ohio
Cemantha Sampson	15	F				Ohio
Nancy Sampson	14	F				Ohio
Rebecca Sampson	12	F				Ohio
Sally Sampson	8	F				Ohio

Listed next to John SAMPSON (æ 30, b. OH) and his wife and family.  There are several NEAL and ROSE families nearby.

5.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).