Secondary sources have Joshua's first name as "Dyer," but I've yet to find a primary record using that name.

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

Cobb, Joshua	Mims, Julia	Jun 23, 1835	Caldwell Co., KY
Cobb, Joshua	Dortch, Maina D.	Jan 18, 1843	Montgomery Co., TN

2.  1840 Census Index and Digital Images (online at Ancestry.com; Image #70-71 of 80; extracted by Diana Gale Matthiesen):

1840

TN

Stewart Co.

pp. 344A-344B

Joshua Cobb

100 101 - 200 010

010 000 - 010 000

0000001

These data indicate:es

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 white male	4 or under	1835-1840	= Robert (b. 1840)
1 white male	15-19	1820-1825	= ?
1 white male	30-39	1800-1810	= Joshua (b. 1809)
2 white females	4 or under	1835-1840	= Irene (b. 1838) = Daughter A (b. ca. 1836/7)
1 white female	20-29	1810-1820	= Julia (b. 1812)
1 male slave	10-23	1816-1830	= ?
1 female slave	10-23	1816-1830	= ?
1	persons employed in learned professions and engineering

The teenage boy is too old to be their son.

3.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  Stewart Co., TN, p. 461B, 1133/1133, enumerated 5 Dec 1850 (extracted by Diana Gale Matthiesen — this record is very difficult to read):

Joshua Cobb	41	m	phisician	5,000	Ky
Marina   "	39	f			Tens
Irine    "	12	f			Ky
Robert   "	10	m			Tens
Edwin    "	7	m			"
Mary     "	6	f			"
Marina   "	4	m			"
Virginia "	3	f			"
Sallie   "	1	f			"
George Dorth	22	m	phissician		"
William	11	m	Student		"

Irene and Robert are Joshua's children by his first wife, Julia MIMS.  George and William are Marina's children by her first husband, William DORTCH.

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

5.  Terry Reigel.  Reigel Roots. [link died]