1
2.  Jordan R. Dodd.  Marriage Index:  Michigan and Wisconsin, 1830-1900.  Liahona Research, Orem, UT (Broderbund CD-251):  not found, and at least some Hillsdale County records were included on the CD.

3.  1850 Census Index/Images (online at Ancestry.com; Image #28 of 33):  Litchfield Twp., Hillsdale Co., MI, p. 431B, 204/211, enumerated 3 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

Elisha E Murry	32	M		Farmer	2000	NY
Mary J Murry	28	F				NY
[Elisha's children, et al.]
James N Robards	19	M		Farmer		Mich

Mary Jane (ROBARDS) MURRAY is James's sister. 

4.  1860 Census Every-Name-Index/Images (online at Ancestry.com, Image #20 of 28):  Quasqueton P.O., Liberty Twp., Buchanan Co., IA, Roll M653_313, p. 529, PN 47, 332/322, enumerated 16 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

James Roberts	28	M		Farmer	600	125	Mich
Kate Roberts	24	F					Mass
Frank Roberts	3	M					Iowa

5.  Library of Michigan 1870 Census Index and Images (online at the Library of Michigan [link died]):  Hillsdale P.O., City of Hillsdale, Fourth Ward, Hillsdale Co., MI, p. 346B, PN 4, enumerated 16 Jun 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

29	26	Roberts James	37	M	W	Farmer	2500	300	Michigan
		_______ Kate	32	F	W	Keeping House			Massachusetts
		_______ Frank	12	M	W	At School			Iowa
	27	Roberts John	40	M	W	Farmer	400	300	Michigan
		_______ Sarah A	32	F	W	At Home			New York
		_______ Jessie	3	F	W	"   "			Michigan

John ROBERTS/ROBARDS is James's brother.

6.  1880 United States Census and National Index (LDS Family History Resource File: CD-ROM Library):

Census Place: Hillsdale, Hillsdale, Michigan
Source: FHL Film 1254580; NARA Film T9-0580; Pg 135B
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
James N. ROBARDS	Self	M	M	W	47	MI	Farmer	--	--
Mary E. ROBARDS	Wife	F	M	W	28	MI	Keeping House	NY	NY
Hattie MARSH	Dau	F	S	W	11	OH		--	--

Hattie must be adopted.  I would have taken her for Mary's child from a former marriage (although Mary's very young to be her mother), but in the 1900 census, Mary states she had no children — or did she take the question to mean only her children with James?  I might also have taken Hattie to be Mary's younger sister, except Mary's maiden name is said to be TERWILLIGER.  I'm unable to find Hattie in the 1870 census, at least not one near her age born in Ohio. 

7.  1890 Census:  the 1890 Census Population Schedules were destroyed.

8.  1900 Census Index/Microfilm (online at Genealogy.com):  Hillsdale Twp., Hillsdale Co., MI, p. 146B, SN 2B, SD 3, ED 90, enumerated 5 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):

1900:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	19	20	22	23	24	25	26	27	28
47	49	Robards Janes?	Head	W	M	Aug 1832	67	M	23			MI	NY	NY	Farmer	0	Y	Y	Y	O	F	F	48
		_______ Mary E	Wife	W	F	Apr 1852	48	M	23	0	0	MI	NY	NY			Y	Y	Y

Listed two households from son, Frank P. ROBARDS.

2.  Messages in the Robards Family Genealogy Forum (online at GenForum.com).  One message includes an excerpt on the ROBARDS family from the following source:

2a.  Vivian Lyon Moore.  1933.  Lineages of Some Early Hillsdale County Families.  Typescript MS.