Said to have had only these two children.

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

Cobb, Caleb C.

Machen, Mary W.

2 Dec 1822

Caldwell Co.

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

Calib C. COBB Spouse: Mary W MACHIN Marriage: 2 Dec 1822, Caldwell, Kentucky Source: patron submission

Caleb C. COBB Spouse: Mary Ann WARD Marriage: 2 Dec 1822, Mason, Kentucky Source: patron submission

Unfortunately, the latter record is leading people astray.

2.  1830 Census Index and Digital Images (online at Ancestry.com; Image #79-80 of 88; extracted by Diana Gale Matthiesen):

1830

KY

Caldwell Co.

pp. 176B-177A

C.C. Cobb

200 002 - 000 010

120 100 - 410 000

These data indicate:

No., Race, Gender	Age Class	Therefore Born	Individuals Inferred
2 white males	4 or under	1825-1830	= ? = Thomas (b. 1826/7)
2 white males	30-39	1790-1800	= Caleb (b. 1796/7) = ?
1 white female	20-29	1800-1810	= Mary (b. 1804)
1 male slave	9 or under	1820-1830	= ?
2 male slaves	10-23	1806-1820	= ? ?
1 male slave	36-54	1775-1794	= ?
4 female slaves	9 or under	1820-1830	= ? ? ? ?
1 female slave	10-23	1806-1820	= ?

It's hard to say who the other adult white male is; Caleb has no known brothers in this age class.  Caleb is said to have had only one son, so does the boy belong to the other adult male?  Listed 16 lines above Samuel GLENN.

3.  1840 Census Index and Digital Images (online at Ancestry.com; Image #49-50 of 94; extracted by Diana Gale Matthiesen):

1840

KY

Caldwell Co.

pp. 25B-26A

Cobb C C

002 341 - 000 000

2/16/17 15/6/0 - 231 000

8006000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 white males	10-14	1825-1830	= ? = Thomas (b. 1826/7)
3 white males	15-19	1820-1825	= Giles (b. 1823) = ? = ?
4 white males	20-29	1810-1820	= Gideon (b. 1817/8)  = ? = ? = ?
1 white male	30-39	1800-1810	= Caleb Clark (b. 1796/7)
2 male slaves	9 or under	1830-1840	= ? ?
16 male slaves	10-23	1816-1830	= ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
17 male slaves	24-35	1804-1816	= ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
15 male slaves	36-54	1785-1804	= ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
6 male slaves	55-99	1740-1785	= ? ? ? ? ? ?
2 female slaves	9 or under	1830-1840	= ? ?
3 female slaves	10-23	1816-1830	= ? ? ?
1 female slave	24-35	1804-1816	= ?
8	persons employed in mining
6	persons employed in manufacture and trades

It appears this census record may be of Caleb's place of business (viz., the iron works), which also served as residence.  Caleb is in the wrong age class, but there can be no doubt this is our subject.  Mary has died, and it appears he daughter, Ellen, has been placed with other members of the family (with obvious good reason), but his son, Thomas, appears to be with him.  Caleb's parents died in the 1830s, so his two unmarried brothers, Gideon and Giles, appear to be living with him.  Hard to say who the others are.  If only 14 persons were "employed," what were all the slaves for?

4a.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  District No. 1, Crittenden Co., KY, p. 223B, 195/195, enumerated 29 Aug 1850 (extracted by Diana Gale Matthiesen):

Gideon D Cobb	32	M	Merchant & Iron m	30000	Kentucky
Caleb C Cobb	53	M	Iron maker		Vermont
James Durham	21	M	L		Tenn
Albert   "	13	M	L		"
Gabrel Jarrel	20	M	L		Ky

Gideon Dyer COBB is Caleb's brother.  They are living next door to their sister, Persis (COBB) MARSHALL. 

4b.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  District No. 1, Caldwell Co., KY, p. 321A, 611/611, enumerated 7 Sep 1850 (extracted by Diana Gale Matthiesen):

Clark C Cobb	55	M	Iron Master	1000	Caldwell cty Ky
John C    "	13	M			"
Gideon B  "	4	M			"
Louisa P? Long	37	F			"
Sarah      "	70	F			Nelson cty Ky
David Lackman	18	M	Labourer		Tennessee

Caleb Clark COBB has managed to get himself enumerated twice — it does happen occasionally.  Caleb's son, Thomas J. COBB (æ 23, b. Caldwell Co., KY), is married and living with his wife, Almeda (æ 22, b. Caldwell Co., KY), in Caldwell Co., KY; Caleb's daughter, Ellen M. COBB (æ 14, b. Caldwell Co., KY), is living with her maternal grandparents, Henry & Nancy MACHEN, in Caldwell Co., KY.

5.  J.H. Battle, W.H. Perrin, & G.C. Kniffin.  1887. Kentucky, a History of the State.  F.A. Battey & Co., Louisville, KY (excerpts online at the Kentucky Biographies Project [link died]):

EX-UNITED STATES SENATOR, WILLIS B. MACHEN ... Leaving school, he engaged in the manufacture of iron with C.C. Cobb, in Livingston County, in which he was engaged for seven years, and in 1838 entered the mercantile business...

Crittenden Co. wasn't formed from Livingston Co. until 1842, so at the time, the business was in Livingston Co.

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

7.  Terry Reigel.  Reigel Roots. [link died]  Plus emails.

8.  Email from Marsha M. Cobb, who says a 1930 family letter indicates our subjects had only two children:  Thomas Jefferson COBB and Ellen M. COBB.