Valentine was in Ohio by 1807, so either William is mistaken about being born in VA or he was not born in 1808.

1.  Anon.  1966.  Marriage Index:  Ohio, 1789-1850.  Liahona Research, Orem, UT (Broderbund CD-400):  not found.

2.  1840 Census Index and Digital Images (online at Ancestry.com; Image #18-19 of 24 — the numerical data pages precede the name pages; extracted by Diana Gale Matthiesen):¤•

1840

OH

Fairfield Co.

Walnut Twp.

pp. 351A-351B

Ln. 1

Cupp William

200 011 - 010 010

0100000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	4 or under	1835-1840	= Son B = Son A
1 male	20-29	1810-1820	= ?
1 male	30-39	1800-1810	= William (b. 1808)
1 female	5-9	1830-1835	= Mary (b. 1834)
1 female	20-29	1810-1820	= Catharine (b. 1812)
1	person engaged in agriculture

"Sons" A and B could be James and Preston, as found in the 1850 census; then again, without them, there is a nine year gap with no children, so an additional two sons makes more sense.  List is roughly alphabetized, so no neighborhood reconstruction is possible.  Also, for reasons known only to the microfilmer, the page spreads were photographed in reverse order.  Because only the front sides of the pages (the ones with the data, but no names) have page numbers, the consequence of being photographed in reverse order is that it's difficult to be specific as to the page number where a name is found.

3.  1850 Census Index/Images (online at Ancestry.com; Image #47-48 of 51):  Walnut Twp., Dist. 41, Fairfield Co., OH, pp. 219A-219B, 1328/1328, enumerated 6 Sep 1850 (extracted by Diana Gale Matthiesen):¤•

Cupp William	42	M	Farmer	960	Va
"  Catharine	38	F			"
"  Mary Ann	16	F			O
"  Elizabeth	6	F			"
"  George W	2	M			"
Rayam? James	14	M			"
[next page]
Rays D Presten	14	M			O
Fall George	33	M	Farmer		Va
"  Elizabeth	43	F			"

Living next door to William's father, Valentine CUPP. 

4.  1860 Census Images (online at Ancestry.com; Image #5 of 54):  Pleasantville P.O., Walnut Twp., Fairfield Co., OH, p. 227A, PN 187, 1367/1366, enumerated 3 Aug 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):¤•

Wm Cupp	52	M		Farmer	2000	900	Va
Catharine "	49	F					Do
Elizabeth C "	17	F					Ohio
George W    "	12	M					Do
Elizabeth Fall	53	F		Serving			Va
George Fall	42	M		Farmer			Do

Living next to William's widowed step-mother, Barbara (KELLER) CUPP. 

5.  1870 Census Index/Images (online at Genealogy.com; Image #24 of 42):  Adrian P.O., Seneca Twp., Seneca Co., OH, Roll 1266 (Book 1), p. 271B, PN 24, 207/190, enumerated 20 Jun 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Culp William	63	M	W	Farmer	8000	4000	Penn
____ Cath	54	F	W	Keeps House			Va
____ Eliz	27	F	W				O
____ George	22	M	W	Farm Lab			O
Cruiuer? Chas	28	M	W	"   "			Md

6a.  LDS.  Family Search: Census Records: 1880 United States (online at FamilySearch.org):¤•

Census Place: 3rd Ward, Tiffin, Seneca, Ohio
Source: FHL Film #1255065; NARA Film #T9-1065; Pg 212C
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
William CUPP	Self	M	M	W	72	VA	Farmer	VA	VA
Katherine CUPP	Wife	F	M	W	65	VA	K. H.	VA	VA
Geo. W. CUPP	Other	M	M	W	31	OH	Grocer	VA	VA

Is George estranged from his wife?

6b.  1880 Census Images (online at Ancestry.com; Image #19 of 41):  Market Street, City of Tiffin (Ward 3), Seneca Co., OH, p. 212C, PN 19, SD 1, ED 203, 192/192, enumerated 8 Jun 1880, official enumeration date 1 Jun 1880:  George's "Relation" is simply blank; his status is married.

7.  Anon.  1886.  History of Seneca County, Ohio.  Warner, Beers & Co., Chicago (online at Heritage Pursuit):

p. 857

Hopewell Township WILLIAM CUPP, retired farmer, Tiffin, was born May 7, 1808, in Augusta County, Va., son of Valentine and Mary (Fall) Cupp, of German descent.  Valentine Cupp was twice married and had nine children, of whom six survive, two — David and William — being residents of Ohio.  Our subject was brought to Fairfield County, Ohio, by his parents in 1808, his father carrying him in front of him on his horse most of the way.  They settled in Walnut Township, Fairfield Co., Ohio, where the father purchased a farm on which he passed the remainder of his life.  Our subject was educated in Fairfield County and was there united in marriage with Miss Catharine Fall (a second cousin), by whom he had three children: Mary A., now the widow of Joel Keller (has two children); Elizabeth C., wife of William Orme (have four children); and George W., married to Lucy Fisher; they reside in Tiffin and have one child living.  Mr. Cupp bought a fine farm in this county, and moved here in 1865.  Retiring from same in 1877, he came to Tiffin, where he now lives, having bought a fine property on Market Street.  He has been a successful farmer, and is a fine gentleman. He is a member of the first Reformed Church, of Tiffin. Col. Valentine Cupp, of the First Ohio Volunteer Cavalry, a brother of our subject, was killed at the battle of Chickamauga in September, 1863.

Valentine is on the 1807 tax list of Fairfield Co., OH.

8.  Broderbund.  World Family Trees.  Vol. 25, Pedigree #1709.