1.  D.L. Murray & N.R. Murray, compilers.  1996. Marriage Index: AR, MO, MS, TX, 1766-1981.  Marriage data from the "Hunting for Bears" collection (Broderbund CD-5):

SINGLETON, Otho R	FIELD, Martha A.	1843-Aug-22	Madison, MS
SINGLETON, Otho R	LAUGHBOROUGH, Eliza P Mrs	1859-Nov-08	Yazoo, MS

She is the only LAUGHBOROUGH on the CD.  It is an extremely rare surname.  We ought to be able to find her first marriage record.

2.  1850 Census Images (online at Ancestry.com; Image #27 of 104):  Madison Co., KY, p. 143A, 183/185, enumerated 27 Aug 1850 (extracted by Diana Gale Matthiesen):

Otho R Singleton	35	m	Lawyer	3500	Kentucky
Martha A   "	26	f			Virginia
Richard H  "	6	m			Missi
Thomas T   " Jr	1	m			Ditto
Thomas T   " Sr	25	m	Lawyer		Kentucky

Thomas Sr. is almost certainly Otho's brother.

3.  1860 Census Images (online at Ancestry.com; Image #128 of 133):  City of Canton, Madison Co., MS, p. 910, PN 128, 903/902, enumerated 3 Oct 1860 (extracted by Diana Gale Matthiesen):

O.R. Singleton	45	M	W	Lawyer & Member of Congress	5000	25000	Kenn.
Eliza Y.  "	32	F	W		12000	20000	Tenn.
Thos. T   "	11	M	W				Miss.
R.H.      "	16	M	W				"
Kate F.   "	8	F	W				"
Christina McIlree?	23	F	W	House keeper			"

4a.  Census Index:  U.S. Selected Counties, 1870 (Broderbund CD-319):  there are no MS records on the CD.

4b.  AIS (Accelerated Index System) Census Index (online at Ancestry.com):  found only in 1850.

5a.  1880 United States Census and National Index (LDS Family History Resource File: CD-ROM Library):

Census Place: Washington, Washington, D.C., Washington D.C.
Source: FHL Film 1254123; NARA Film T9-0123; Pg 209D
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
Mary A. MOORE	Self	F	W	W	52	PA	Keeping House	HANOVER	PA
Frank MOORE	Son	M	S	W	27	VA	Painter	CAN	PA
Edward MOORE	Son	M	S	W	25	VA	Painter	CAN	PA
Charles S. MOORE	Son	M	S	W	21	VA	Lawyer	CAN	PA
Otho R. SINGLETON	Other	M	M	W	64	KY	M.C.	KY	KY
Eliza Y. SINGLETON	Other	F	M	W	50	TN	At Home	TN	TN
James B. BECK	Other	M	M	W	58	SCO	U.S. Senator	SCO	SCO
Jane A.J.W. BECK	Other	F	M	W	53	VA	At Home	VA	VA
James P. HORBACK	Other	M	M	W	53	PA	Farmer	PA	PA
Mary C. HORBACK	Other	F	M	W	44	VA	At Home	PA	VA
Mary C. HAZEN	Other	F	W	W	28	PA	Clerk In Treasury	VA	MD
Henry HEAD	Other	M	M	W	58	ENG	Retired Merchant	ENG	ENG
Lotta HYATT	Other	F	W	MU	23	MD	Servant	MD	MD

5b.  1880 Census Images (online at Ancestry.com; Image #16 of 38):  1307 F Street North West, Washington, Washington Co., District of Columbia, p. 209D, PN 16, SD 17, ED 54, enumerated 7 Jun 1880 (extracted by Diana Gale Matthiesen).  Except for the street address and E.D., etc., the film doesn't tell us any more than the LDS transcription, except that the original said "boarder" where the LDS used "Other."

6.  The Political Graveyard:

Singleton, Otho Robards (1814-1889) of Canton, Madison County, Miss.  Born near Nicholasville, Jessamine County, Ky., October 14, 1814.  Democrat.  Member of Mississippi state house of representatives, 1846; member of Mississippi state senate, 1848; Presidential Elector for Mississippi, 1852; U.S. Representative from Mississippi, 1853-55, 1857-61, 1875-87 (3rd District 1853-55, 4th District 1857-61, 1875-83, 5th District 1883-87); served in the Confederate Army during the Civil War; Representative from Mississippi in the Confederate Congress, 1862-65.  Died in Washington, D.C., January 11,    1889.  Interment at Canton Cemetery, Canton, Miss. See also: congressional biography.

7.  Biographical Directory of the United States Congress [link died]:

SINGLETON, Otho Robards, a Representative from Mississippi; born near Nicholasville, Jessamine County, Ky., October 14, 1814; attended the common schools; was graduated from St. Joseph’s College, Bardstown, Ky., and from the law department of the University of Lexington; was admitted to the bar in 1838 and commenced practice in Canton, Madison County, Miss.; member of the State house of representatives in 1846 and 1847; served in the State senate 1848-1854; elected as a Democrat to the Thirty-third Congress (March 4, 1853-March 3, 1855); unsuccessful candidate for reelection; elected to the Thirty-fifth and Thirty-sixth Congresses and served from March 4, 1857, until January 12, 1861, when he withdrew; Representative from Mississippi in the Confederate Congress 1861-1865; elected as a Democrat to the Forty-fourth and to the five succeeding Congresses (March 4, 1875-March 3, 1887); was not a candidate for renomination in 1886; died in Washington, D.C., January 11,1889; interment in Canton Cemetery, Canton, Madison County, Miss.

8.  Joey Oller. "Confederate Congressmen of Kentucky." Extracted from Warner & Yearns's Biographical Register of the Confederate Congress (online in the USGenWeb Archives):

Representative	Birth	Burial	State
Otho Robards Singleton	(1814-1889) Jessamine Co., KY	Canton, MS	MISSISSIPPI