Dorcas's mother, Sarah (GREENLAND) SHAW, was the daughter of Nathan GREENLAND & Sarah Ruth CORBIN.  Sarah Ruth was the daughter of Benjamin CORBIN & Sarah SIAS.  I'm going to assume, for the present, that David is related to Benjamin CORBIN because these CORBIN, GREENLAND, and SHAW families intermarried repeatedly.  If David is related to Benjamin, it is most likely as a grandson, but it may be as likely that David is a grandson of Benjamin's brother, William CORBIN, though William was considerably younger than Benjamin, so there are fewer opportunities to fit in a grandson David's age.

— born in PA, either Menno Twp., Mifflin Co., PA, or Harris Twp., Centre Co., PA:
5.  Vienna / Viana M. CORBIN, b. 1851/2
6.  James CORBIN, b. 1853/4; prob. d. bef. 1870
7.  Charles CORBIN, b. 1856/7; d. bef. 1870

— born in PA, either Harris Twp., Centre Co., PA, or Taylor Twp., Fulton Co., PA:
8.  Calvin William Fisher CORBIN, b. 31 May 1861

1.  Marriage Record:

2.  1840 Census Index/Images (online at Ancestry.com):  not found.  (If they're typical newlyweds, they're likely living with either his parents or hers.)

3.  1850 Census Every-Name-Index/Images (online at Ancestry.com, Image #16 of 27):  Menno Twp., Mifflin Co., PA, Roll M432_797, p. 230B, 113/113, enumerated 6 Sep 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):¤•

David Corbin	29	M		Laborer		Pa
Dorcas    "	31	F				"
Mary      "	9	F				"
Milton    "	5	M				"
Alonzo C  "	3	M				"
Henrietta "	2/12	F				"

4.  1860 Census Every-Name-Index/Images (online at Ancestry.com, Image #23 of 49):  Boalsburg P.O., Harris Twp., Centre Co., PA, Roll M653_1090, p. 573, PN 119, 855/879, enumerated 7 Jul 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):¤•

David Corbin	29	M		Day Laborer		75	Penna
Dorcas    "	32	F					"
Wilton    "	15	M					"
Alonzo    "	12	M					"
Henrietta "	10	F					"
Vienna    "	8	F					"
James     "	6	M					"
Charles   "	2	M					"

5.  1870 Census Every-Name-Index/Images (online at Ancestry.com, Image #18 of 22 — Fulton County not indexed):  Hustontown P.O., Taylor Twp., Fulton Co., PA, p. 84B, PN 18, 126/125, enumerated 17 Jun 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Corban David H	51	M	W	Farmer	1000	200	Penna
______ Darcas	51	F	W	Keeping House			Penna
______ Viana M	18	F	W	at Home			Penna
______ Calvin W	9	M	W				Penna
Scott Samuel	20	M	W	Farm Labourer			Penna

Listed next to Dorcas's brother, John SHAW (æ 49, b. PA, wife Irene).

6.  1880 Census Every-Name-Index/Images (online at Ancestry.com, Image #14 of 16):  Henderson Twp., Huntingdon Co., PA, Roll T9_1134, p. 131B, PN 22, SD 7, ED 189, enumerated 23 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):¤•

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
2	3	4	5	6	8	9	11	24	25	26
6	Corbin Dorathey	W	F	65			\	Penna	Penna	Penna
	______ Calvin W	W	M	19	Son	\		"	"	"

Dorathey?

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

8.  1900 Census Every-Name-Index/Images (online at Ancestry.com):  not found.

9.  OneWorldTree (online at Ancestry.com).

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

11.  Messages posted to the Corbin Family Genealogy Forum (online at GenForum.com).