— born in KY²:
  4.  John SELLS, Jr., b. 9 Dec 1802, KY; m. 12 Jan 1823, Franklin Co., OH, Merenia/Marindu HUTCHINSON

— born in Washington Twp., Franklin Co., OH:
  5.  Samuel SELLS, b. 12 Sep 1804; m. 6 Oct 1825, Clermont Co., OH, Susannah "Susan" RICHEY
  6.  Catherine SELLS, b. 28 Dec 1806; m. 20 Oct 1824, Franklin Co., OH, Stephen GRACE
  7.  Fletcher SELLS, b. 16 Aug 1809; m. 1829, Franklin Co., OH, Nancy GORTON
  8.  Lucy SELLS, b. Sep 1814; m. 10 Jan 1833, Franklin Co., OH, Albert CHAPMAN
  9.  Caroline SELLS, b. 1817/8
10.  (Son A) SELLS³, b. 1815-20

²It shouldn't surprise us that one (or more) of the children was born in KY.  Elizabeth's brother, Anthony STROUP, also made his way to OH via KY:  Anthony married in Mason Co., KY, in 1804, then was in Highland Co., OH, by 1806. 

³I had thought "Son A" might be Francis SELLS (b. 1819), but apparently Francis is the son of John's brother, William.

1a.  Marriage Record:

1b.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org):
While I haven't found John SELLS in any PA census, his father was in the 1790 census of Huntingdon Co., PA, so the econdary sources (on WorldConnect) claiming the children's births were in Huntingdon Co., PA — not York Co., PA — would seem to be the correct ones.

Charles SELLS Birth: 1794, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Charles SELLS Birth: 1794, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	Charles SELLS Spouse: Amanda HUTCHESSON Marriage: 7 Mar 1822, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
Elind SELLS — this is a mis-reading of Eliud Birth: 18 Oct 1796, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Elind SELLS — this is a mis-reading of Eliud Birth: 18 Oct 1798, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	Eliot SELLS — this is a mis-reading of Eliud! Spouse: Polly SELLS Marriage: 20 Aug 1820, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
Mathilda SELLS Birth: 11 Jun 1799, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Mathilda SELLS Birth: 11 Jun 1799, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	Matilda SELLS Spouse: William KILBOURN Marriage: 31 Oct 1822, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
John SELLS Birth: 9 Dec 1802, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	John SELLS Birth: 1 Dec 1802, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	John SELLS Spouse: Merenia HUTCHINSON Marriage: 12 Jan 1823, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
John was born in KY and Samuel in OH, so the family moved from KY to OH sometime between 1802 and 1804.
Samuel SELLS Birth: 12 Sep 1804, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Samuel SELLS Birth: 12 Aug 1808, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	Samuel SELLS — this may be our subject; he's in 1850 census of Brown Co., OH (æ 46, b. OH) Spouse: Susana RICHEY Marriage: 6 Oct 1825, Clermont, Ohio Source: Marriage Records, 1801-1910. Probate Court (Clermont County)
Catherine SELLS Birth: 28 Dec 1806, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]		Catharine SELLS Spouse: Stephen GRACE Marriage: 20 Oct 1824, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
Fletcher SELLS Birth: 16 Aug 1809, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Fletcher SELLS Birth: 10 Aug 1809, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	FLETCHER SELLS Spouse: NANCY GORTON Marriage: 1829, <of Dublin>, Franklin, Ohio Source: [patron submission]
Lucy SELLS Birth: 19 Sep 1814, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]	Lucy SELLS Birth: 19 Sep 1814, Of, York, Pennsylvania Father: John SELLS; Mother: Elizabeth STROUP Source: patron submission	Lucy SELLS Spouse: Albert CHAPMAN Marriage: 10 Jan 1833, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)
Caroline SELLS Birth: 11 Jan 1817, Dublin, Franklin, Ohio Father: John SELLS JR.; Mother: Elizabeth STROUP Source: [patron submission]		Caroline SELLS Spouse: Tenis HUTCHINSON Marriage: 5 Jan 1835, Franklin, Ohio Source: Marriage Records, 1803-1951. Ohio. Probate Court (Franklin County)

2.  1790 Census Index and Digital Images (online at Ancestry.com):  I examined every page of Huntingdon Co., PA.  Our subject is not yet married, so does not appear as head-of-household.  The following SELLS were in Huntingdon Co., PA:  John's father, "Lodawick" SELL (3-3-4-0-2, p. 1/110, mis-indexed "Sill" — there is room in his household for his unmarried son, John), Henry SILL (p. 6/120), Solomon SILL (p. 6/120), John SELL (2-1-2-0-0, p. 9/126, too old to be our subjects because they already have two children), and Abraham SELL (p. 10/128).  The only other possibility is that we are very wrong about John's and Elizabeth's birthdates (from their tombstones), and that they did marry and have two children by 1790, which would also explain William.

3.  Anon.  1991.  The 1795 Census of Kentucky [as constructed from tax lists].  T.L.C. Genealogy, Miami Beach, FL (said to include every extant tax list from every county existing in the state of Kentucky in 1795):  not found.

4a.  1800 Census Index and Digital Images (online at Ancestry.com):  not found.  I examined every page of Huntingdon Township/Borough, and the only John SILLS/SELLS I found there was too old to be our subject and had three daughters (our subject should have two sons and one daughter).

4b.  Census Index:  U.S. Selected Counties, 1800 (Broderbund CD-312):  there was no 1800 census in OH, and the 1800 census of KY was lost (though tax lists are substituted on this CD for some KY counties).  The 1800 census of PA is extant, but neither Ludwick nor our John was in it.  It appears they were in Kentucky in 1800.

1806 Tax List	Sills, Lodwick	OH	Franklin Co.		p.  9
1807 Tax List	Sells, Ludwick	OH	Franklin Co.		p. 14
1808 Tax List	Sells, Lowick	OH	Franklin Co.	Mixed Twps.	p. 21
1809 Tax List	Sells, Ludwick	OH	Franklin Co.	Washington Twp.	p. 23
1809 Tax List	Sells, John	OH	Franklin Co.	Washington Twp.	p. 23

It's probable that John was living with his father, Ludwick SELLS, in 1806-1808.

5.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313):  the 1810 census of Ohio was lost, except for Washington County.  Tax lists for some Ohio counties are substituted on this CD, but not for Franklin County.

6.  1820 Census:  the 1820 Franklin Co., OH, census schedules were lost, which is most unfortunate because it means we have no early census data for our subjects.

7.  1830 Census Index and Digital Images (online at Ancestry.com; Image #1 of 6; extracted by Diana Gale Matthiesen):¤•

1830

OH

Franklin Co.

Town of Dublin [in Washington Twp.]

p. 17

Ln. 11

John Sells Sr

001 000 010 - 001 100 010

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	10-14	1815-1820	= Son A
1 male	50-59	1770-1780	= John (b. 1774)
1 female	10-14	1815-1820	= Caroline (b. 1817/8)
1 female	15-19	1810-1815	= Lucy (b. 1814)
1 female	50-59	1770-1780	= Elizabeth (b. 1777)

Listed three lines from William SELLS (211 201 - 021 101), who is next to son, Charles SELLS (100 101 - 010 010), who is next to son, Eliud SELLS (100 101 - 200 001), who are also in the Town of Dublin.  In the other direction, listed 15 lines from son, John SELLS, Jr. (100 010 - 110 010), who is next to son, Fletcher SELLS (100 010 - 000 010), both of whom are in Washington Twp. (i.e., not in the Town of Dublin).

8.  1840 Census Index and Digital Images (online at Ancestry.com; Image #3-4 of 4; extracted by Diana Gale Matthiesen):¤•

1840

OH

Franklin Co.

Town of Dublin [in Washington Twp.]

pp. 121B-122A

Ln. 8

John Sells

000 000 001 - 001 000 001

0100000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	60-69	1770-1780	= John (b. 1774)
1 female	10-14	1825-1830	= ?
1 female	60-69	1770-1780	= Elizabeth (b. 1777)
1	person engaged in agriculture

Hard to say who the girl is; she is too young to be their daughters, but she could be other kin or hired help.  Listed four lines from son-in-law, "Z. HUTCHESON."

9.  1850 Census Index/Images (online at Ancestry.com; Image #29 of 33):  Dublin, Washinton Twp., Dist. 38, Franklin Co., OH, p. 189A, 219/220, enumerated 17 Sep 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):¤•

Zenas Hutchinson	35	M		Landlord	1800	O
_____ Caroline	32	F				"
_____ Byron	9	M				"
_____ Hel????	2	M				"
Joseph Niewsanger?	21	M		Wagon Maker		Va
Elizabeth Sells	60	F				Md
Nathanial Butcher	21	M	B	Hostler		Va
John Depp	19	M	B	Cook		"
Matilda Davies	12	M				O
Clark Davies?	5	M				"

Caroline (STROUP) HUTCHINSON is Elizabeth's daughter.  Elizabeth's age is off (she should be 72), but there can be no doubt this is our subject — and widows do lie about their age.  Also in Washington Township:  William SELLS (æ 59, b. PA, wife Elizabeth, p. 176A), son Fletcher SELLS (æ 41, b. OH, wife Nancy, p. 183B), son John SELLS (æ 47, b. KY, wife Marindu, p. 183B), and nephew Francis SELLS (æ 30, b. OH, wife Mary, p. 188A — mis-indexed as Benjamin).  The Samuel SELLS (æ 21, b. OH, p. 136B) in Norwich Twp., Franklin Co., OH, is too young to be their son.  There is a Samuel SELLS (æ 46, b. OH, wife Susan, p. 466A) in Lewis Twp., Brown Co., OH, who appears to be the Samuel who is their son.

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