If Henry is the brother of the Mathias SLYH — who also came from (W)VA and appears in the Franklin Co., OH, census for the first time in 1830 — they would obviously have the same parents, though those parents are in dispute.  Basically, it's a question of whether Mathias is the son or grandson of Joh. Friedrich SCHLEICH.

Given Henry's age, he almost certainly had an earlier wife, just as Susanna had an earlier husband.  If our subject is the Henry SLEIGH in the 1810 census of Jefferson Co., (W)VA, then he clearly did have an earlier wife — and children.

Did our subject also marry Mary?  Is "Daughter B" her child?

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

Henry SLIGH Spouse: Mary HIGGINS Marriage: 16 Aug 1821, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)

Henry SLY Spouse: Susan HOPPER Marriage: 6 Feb 1823, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)

2.  1810 Census Index and Digital Images (online at Ancestry.com; Image #14 of 28; extracted by Diana Gale Matthiesen):

1810

VA [now WV]

Jefferson Co.

p. 84

Henry Sleigh

11010-10010-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1800-1810	= Son A
1 male	10-15	1794-1800	= ?
1 male	26-44	1765-1784	= Henry (b. 1780-84)
1 female	9 or under	1800-1810	= Daughter A
1 female	26-44	1765-1784	= Wife-1

If this Henry is our subject — he may not be — he is probably too young to have had a child by 1800.  The other children would have been married and gone by 1830.  Listed next to Mathias SLEIGH/SLYH. 

3.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  can't find.  The Henry SLY in Brown Co., OH, is there through 1860 (i.e., is not our subject).  Having been widowed, Henry and his children may be living with other family members, possibly not even together.  Mathias SLEIGH/SLYH is still in Jefferson Co., (W)VA. 

4.  1830 Census Index and Digital Images (online at Ancestry.com; Image #7 of 8; extracted by Diana Gale Matthiesen):

1830

OH

Franklin Co.

Prairie Twp.

p. 22

Henry Sly

120 100 100 - 010 010 100

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	4 or under	1825-1830	= Jacob SLY (b. 1827/8)
2 males	5-9	1820-1825	= Henry Clay SLY (b. 1823/4) = Edward HOPPER (b. 1820)
1 male	15-19	1810-1815	= John HOPPER (b. 1810)
1 male	40-49	1780-1790	= Henry SLY
1 female	5-9	1820-1825	= Daughter B SLY (b. 1823-25)
1 female	20-29	1800-1810	= Margaret HOPPER (b. 1809/10)
1 female	40-49	1780-1790	= Susan (NEFF) HOPPER SLY (b. 1781/2)

Listed three lines from Isaac NEFF.  The only other SLY/etc. in Franklin County is Mathias SLY/SLYH in Clinton Township. 

5.  1840 Census Index and Digital Images (online at Ancestry.com; Image #3-4 of 10; extracted by Diana Gale Matthiesen):

1840

OH

Franklin Co.

Prairie Twp.

pp. 146B-147A

H. Sligh

001 111 010 - 000 100 010

0200000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	10-14	1825-1830	= Jacob SLY (b. 1827/8)
1 male	15-19	1820-1825	= Henry Clay SLY (b. 1823/4)
1 male	20-29	1810-1820	= Edward HOPPER (b. 1820)
1 male	30-39	1800-1810	= John HOPPER (b. 1810)
1 male	50-59	1780-1790	= Henry SLY
1 female	15-19	1820-1825	= Daughter B SLY (b. 1823-25)
1 female	50-59	1780-1790	= Susan (NEFF) HOPPER SLY (b. 1781/2)
2	persons engaged in agriculture

6.  1850 Census Index/Images (online at Ancestry.com; Image #22 of 26):  Dist. 38, Prairie Twp., Franklin Co., OH, p. 120A/239, 156/157, enumerated 7 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

Clay Sly	26	M		Farmer	1100	Va
Hannah	17	F				Pa
Susan	68	F				Va
John Hopper	40	M				"

Henry Clay was born in Ohio (see his 1860 and 1870 census records); Hannah appears to be his wife, though her name is supposed to be Margaret.  John is Susan's son from her first marriage.  Living next door to Susan's son, Edward HOPPER (æ 30, b. OH, wife Rebecca), who is three doors from our subjects' son, Jacob SLY (æ 22, b. OH, wife Margarett).

7.  1860 Census Images (online at Ancestry.com; Image #33 of 36):  Village of Rome, Prairie Twp., Franklin Co., OH, p. 228A/455, PN 165, 1153/1111, enumerated 3 Aug 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

Susan Sly	74	F			2000	400	Va
John Hopper	35	M					"
Amanda Sly	9	F					O
John Robinson	52	M		Farmer	300		?

Amanda is Susan's granddaughter (daughter of Henry Clay SLY and his first wife).

8.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).