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

Marshall, George M.

Cobb, Peris

11 Feb 1834

Caldwell Co.

2.  1840 Census Index and Digital Images (online at Ancestry.com; Image #33 of 94; extracted by Diana Gale Matthiesen):

1840

KY

Caldwell Co.

p. 18

Marshall Geo M

110 010 - 100 020

010 000 - 001 000

0300000

These data indicate:s

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 white male	4 or under	1835-1840	= Edwin (b. 1836/7)
1 white male	5-9	1830-1835	= John (b. 1833/4)
1 white male	20-29	1810-1820	= George (b. 1812/3)
1 white female	4 or under	1835-1840	= Ellen (b. 1838/9)
2 white females	20-29	1810-1820	= Aurelia (b. 1819/20) = Persis (b. 1812/3)
1 male slave	10-23	1816-1830	= ?
1 female slave	24-35	1804-1816	= ?
3	persons employed in agriculture

Persis's parents died in the 1830s, so it looks like her unmarried sister, Aurelia, is living with them.  Listed three lines above Samuel GLENN.

3.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  District No. 1, Crittenden Co., KY, p. 223B, 194/194, enumerated 29 Aug 1850 (extracted by Diana Gale Matthiesen):

George M Marshal	37	M	Clerk		Ky
Perses C    "	37	F			"
John C      "	16	M			Ky
Edwin M     "	13	M			"
Ellen A     "	11	F			"
Gideon D	10	M			"
Henry B?/R? "	5	M			"
Mary E      "	4	F			"
Charles W	2	M			"

Living next door to Persis's brothers, Gideon Dyer COBB and Caleb Clark COBB.