1.  Liahona Research (Orem, UT), compilers.  1996.  Marriage Index:  Ohio, 1789-1850 (Broderbund CD-400):

Horn, Hardman

Porter, Rachel

Sep 25, 1834

Knox Co.

2.  Family Quest Archives:  Ohio Federal Census 1840:  Knox County.  Heritage Quest CD M704-406 (extracted by Diana Gale Matthiesen):

1840

OH

Knox Co.

Brown Twp.

p. 348B

Hertmon Horn

000 010 - 110 010

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	20-29	1810-1820	= Hardman (b. 1811/2)
1 female	4 or under	1835-1840	= Mary (b. 1835)
1 female	5-9	1830-1835	= Susan (b. 1834)
1 female	20-29	1810-1820	= Rachel (b. 1812/3)

This would seem to prove that Susan and Mary are not twins, and the only way they can both be age 15 in October of 1850 is for Susan to have been born late in 1834 (i.e., after Oct 10th).

3.  Family Quest Archives:  Ohio Federal Census 1850: Knox County.  Heritage Quest CD M432-700:  Brown Twp., Knox Co., OH, p. 433A, 2923/2989, enumerated 10 Oct 1850 (extracted by Diana Gale Matthiesen):

Hardman Horn	38	M	Farmer	1500	Unknown
Rachel   "	37	F			Ohio
Susan    "	15	F			do
Mary     "	15	F			do
Kesiah   "	6	F			do
William  "	1/12	M			do