The KELLEY's who were intermarrying with the CORBINs in MD and PA usually spelled their name KELLEY, rather than KELLY.

— born in Huntingdon Co., PA:
  3.  Sarah CORBIN, b. 1797-1800; m. John HIGHT
  4.  Nicholas CORBIN, b. 1802/3; m1. Mary CHILCOTT; m2. Eleanor CRUM
  5.  Abel W. CORBIN, b. 1804/5; m. Mariah __?__
  6.  William Kelly CORBIN, b. 1807
  7.  Eleanor CORBIN, b. 1804-10; m. Amon CHILCOTT
  8.  Mary CORBIN, b. 1810/1; m. Abraham EVANS
  9.  Ruth CORBIN, b. 1810/1; m. Matthew GLASGOW
10.  Micajah CORBIN, Jr., b. 1815; m1. Ellen __?__; m2. Ellen __?__

1.  Letter, dated 19 Jun 1858, from Keziah (GREENLAND) SHANAFELT (click her link for a full transcription) of Clarion Co., PA, to her son, Thomas.  Keziah is a granddaughter of Benjamin & Sarah (SIAS) CORBIN.  The letter is in the possession of  Laurel Shanafelt Powell of Colorado, and Lorinda Clendenon Greenland generously posted a transcription at her web site. 

...Uncle Elijah and Mycajah married sisters, Sarah and Mary Kelly.  They both died in Cassville...

2a.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).

Micajah CORBIN Birth: 1765, Baltimore, Maryland; Death: 29 Jan 1847, Huntingdon, Pennsylvania Father: Benjamin CORBIN; Mother: Sarah SIAS Spouse: Mary KELLY Birth: Abt. 1769 Source: patron submission

2b.  LDS.  Family Search: Internet Genealogy Service: IGI - International Genealogical Index (online at FamilySearch.org).

Micajah CORBIN Birth: 1765, Baltimore, Maryland; Death: 29 Jan 1847 Marriage: About 1793, Baltimore, Maryland Spouse: Mary KELLY Birth: 1774, Baltimore, Maryland Children born in Baltimore, Maryland: Male CORBIN; Birth: About 1794 Female CORBIN; Birth: About 1795 Children born in Huntingdon, Pennsylvania: Sarah CORBIN; Birth: 1797 Male CORBIN; Birth: About 1801 Abel W CORBIN; Birth: 1804; Death: After 1880 Male CORBIN; Birth: 1806 Female CORBIN; Birth: About 1808 Mary CORBIN; Birth: 18 Mar 1811; Death: 27 Feb 1852 Micajah CORBIN; Birth: 1815 Female CORBIN; Birth: About 1817 Female CORBIN; Birth: About 1819 Source: patron submissions

3.  1800 Census Index and Digital Images (online at Ancestry.com; Image #1 of 3; extracted by Diana Gale Matthiesen):¤•

1800

PA

Huntingdon Co.

Springfield Twp.

Roll 40

p. 137

Ln 32

Micajah Corbin

10010-20100-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1790-1800	= Asahel (b. 1799)
1 male	26-44	1755-1774	= Micajah (b. 1765)
2 females	9 or under	1790-1800	= Sarah (b. 1797-1800) = Daughter A
1 female	16-25	1774-1784	= Mary (b. 1774/5)

Micajah is the only CORBIN head-of-household in the township.

3a.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313):  not found.

3b.  1810 Census Index/Images (online at Ancestry.com):  not found, and I did a page-by-page search of Huntingdon County.  He was not the only one missing from this census who should have been there.

4.  1820 Census Index/Images (online at Ancestry.com; Image #6 of 6 — indexed "Muijah"; extracted by Diana Gale Matthiesen):¤•

1820

PA

Huntingdon Co.

Henderson Twp.

Roll 104

p. 71

Ln. 21

Mecijah Corbin

111101-21201-0-300

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1810-1820	= Micajah Jr. (b. 1815)
1 male	10-15	1804-1810	= Abel (b. 1804/5)
1 male	16-18	1801-1804	= Nicholas (b. 1802/3)
1 male	45 or over	in or bef. 1775	= Micajah (b. 1765)
2 females	9 or under	1810-1820	= Ruth (b. 1810/1) = Mary (b. 1810/1)
1 female	10-15	1804-1810	= Eleanor (b. 1804-10)
2 females	16-25	1794-1804	= Sarah (b. 1797-1800) = Daughter A
1 female	45 or over	in or bef. 1775	= Mary (b. 1774/5)
3	persons engaged in agriculture
*In the 1820 Census, the third column is age class 16-18 and the fourth column is age class 16-25; therefore, any individual in column three is duplicated in column four.

5.  1830 Census Index and Digital Images (online at Ancestry.com; Image #85 of 86 — indexed "Michael Corban"; extracted by Diana Gale Matthiesen):¤•

1830

PA

Huntingdon Co.

Henderson Twp.

p. 137

Michage Corban

001 020 001 - 000 111 010

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	10-14	1815-1820	= Micajah Jr. (b. 1815)
2 males	20-29	1800-1810	= Abel (b. 1804/5) = Nicholas (b. 1802/3)
1 male	60-69	1760-1770	= Micajah (b. 1765)
1 female	15-19	1810-1815	= Ruth (b. 1810/1)
1 female	20-29	1800-1810	= Eleanor (b. 1804-10)
1 female	30-39	1790-1800	= Sarah (b. 1797-1800)
1 female	50-59	1770-1780	= Mary (b. 1774/5)

6.  1840 Census Index and Digital Images (online at Ancestry.com; Image #7 of 20; extracted by Diana Gale Matthiesen):¤

1840

PA

Huntingdon Co.

Henderson Twp.

Roll 462

pp. 206B-207A

Ln 15

Micajah Corbin

000 010 001 - 000 000 001

0200000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	20-29	1810-1820	= Micajah Jr. (b. 1815)
1 male	60-69	1770-1780	= Micajah (b. 1765)
1 female	60-69	1770-1780	= Mary (b. 1774/5)
2	persons engaged in agriculture

Micajah should be in the 70-79 age class.  Listed next to son, Able W. CORBIN, who is listed next to Thomas DEAN. 

7.  1850 Census Every-Name-Index/Images (online at Ancestry.com, Image #6 of 17):  Cass Twp., Huntingdon Co., PA, Roll M432_784, p. 207B, 38/38, enumerated 12 Oct 1850 (extracted by Diana Gale Matthiesen).  It says "Clay" on this one page, but all the pages before and after say "Cass," and the page is indexed as Cass.¤

Nicholas Corbin	47	M		Shoemaker	2500	Pa
Eleanor    "	40	F				"
James H    "	12	M				"
Howard M   "	6	M				"
Mary       "	80	F				Md

8.  1850 Census Every-Name-Index/Images (online at Ancestry.com):  Mary not found; Nicholas is in Cassville, Micajah Jr. and daughter, Mary (CORBIN) EVANS, are in Oneida Twp.

9.  Handwritten "Instrument" found at the Centre County, Pennsylvania, Historical Society (please see this page for transcription and links to scans).

10.  J. Simpson Africa.  1883.  History of Huntingdon and Blair Counties, Pennsylvania.  Louis H. Everts, Philadelphia, PA (online at the Huntingdon County PAGenWeb site; contributed by Mike Gifford):
Under the heading, "Henderson Township":

Micajah Corbin, a native of the State of Maryland, after living a short time on Murray's Run, on the farm now owned by James S. Hall, made a home on the Ridge in Henderson, on a farm which had been occupied by Abraham Corbin.  He died in Trough Creek Valley.  He was the father of Asa, Nicholas, Abel, W.K., and Micajah Corbin.  The latter two are yet residents of Oneida.  Of his daughters, one was married to Capt. Abraham Shore, of Cass township; another to Amon Chilcott, of Trough Creek Valley; a third to Matthew Glasgow, of Brady; another to Abraham Evans, of Henderson; and yet another to John Hight, of the same township.  Her husband died a few years ago at the age of ninety-six years, and she yet resides at Centre Union at the age of eighty-one years. [She since died.]

11.  LDS.  Family Search: Internet Genealogy Service: Ancestral File.  Says Micajah was born in 1765.

12.  Broderbund.  World Family Trees.  Vol. 40, Pedigree No. 356.

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