Although her tombstone says she was born in 1868, it appears she was fibbing about her age later in life — hence, the purchaser of the stone didn't know her true birthyear.  In the 1900 census, her birthyear is shown as 1858 and her age as 42.  The fact that she had no children after 1900 supports the earlier birthyear because the average woman has had her last child by the age of 43.  Had she been only 32 years old in 1900, we would have expected her to have continued to have children for another decade.

My attempts to find Rebecca in the 1880 or earlier censuses, when she's still living with her parents, have so far failed.  Note that she is not the Rebecca Jane "Jennie" ISENBERG who was born in Huntingdon Co., PA, in 1866, nor is she the Rebecca McIlroy ISENBERG (1868-1929) who as born in Huntingdon Co., PA, and married Irvin LEEPER (1867-1920) — see files at WorldConnect and Ancestry Public Member Trees.

1.  Marriage Record:

2.  1890 Census:  the 1890 Census Population Schedules were destroyed.

3.  1900 Census Every-Name-Index/Images (online at Ancestry.com, Image #7 of 10):  Juniata Twp., Huntingdon Co., PA, Roll 1414, p. 211A, SN 4A, SD 12, ED 95, enumerated 11 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

21

22

23

24

25

26

27

28

61

65

Corbin William

Head

W

M

Jul 1859

40

M

16

PA

PA

PA

Farmer

0

Y

Y

Y

R

F

51

______ Rebecca

Wife

W

F

Jan 1858

42

M

16

5

5

PA

PA

PA

Y

Y

Y

______ Harry H

Son

W

M

Oct 1885

14

S

PA

PA

PA

At school

6

Y

Y

Y

______ Clara J

Dau

W

F

Nov 1886

13

S

PA

PA

PA

At school

6

Y

Y

Y

______ Ella B

Dau

W

F

May 1889

11

S

PA

PA

PA

At school

5

Y

Y

Y

______ Frank

Son

W

M

Aug 1890

9

S

PA

PA

PA

At school

4

Y

Y

Y

______ Blanche M

Dau

W

F

Nov 1896

3

S

PA

PA

PA

Y

Y

Y

66

Corbin William E

Head

W

M

Jun 1821

78

M

58

PA

PA

PA

Y

Y

Y

O

F

H

______ Mary

Wife

W

F

Apr 1820

80

M

58

10

6

PA

PA

PA

Y

Y

Y

William E. & Mary CORBIN are our subject's parents.

4.  1910 Census Every-Name-Index/Images (online at Ancestry.com, Image #8 of 17):  Penn Twp., Huntingdon Co., PA, Roll T624_1349, p. 176B, SN 7B, SD 13, ED 80, enumerated 5 May 1910, official enumeration date 15 Apr 1910 (extracted by Diana Gale Matthiesen):

1910:  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

17

18

19

20

23

24

25

26

27

28

29

97

103

Corbin William J

Head

M

W

50

M1

25

PA

PA

PA

Eng

Farmer

General Farm

OA

Y

Y

O

F

F

40

______ Rebecca I

Wife

F

W

41

M1

25

5

5

PA

PA

PA

Eng

None

Y

Y

______ Blanche

Dau

F

W

14

S

PA

PA

PA

Eng

None

Y

Y

Y

104

Thom Clara J

Dau

F

W

23

M1

2

2

2

PA

PA

PA

Eng

None

Y

Y

____ E Lucile

GDau

F

W

3

S

PA

PA

PA

None

____ Robert W

GSon

M

W

1 3/12

S

PA

PA

PA

None

Mark Clair

Cousin

M

W

7

S

PA

PA

PA

None

Y

Rebecca is indexed with middle initial, "J.," but her initial here is clearly, "I."  The letter has no descender, while the "J." for William and for Clara has a clear descender.  The initial probably stands for her maiden name, ISENBERG, not her middle name.

5.  1920 Census Every-Name-Index/Images (online at Ancestry.com, Image #8-9 of 15):  Little Valley, Penn Twp., Huntingdon Co., PA, Roll T625_1564, pp. 122B-123A, SN 4B-5A, SD 14, ED 82, enumerated 14/15 Jan 1920, official enumeration date 1 Jan 1920 (extracted by Diana Gale Matthiesen):

1920:  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

16

17

18

19

21

23

25

26

27

28

29

*

Fm

88

89

Corbin W J

Head

O

F

M

W

60

M

Y

Y

PA

PA

PA

Y

Farmer

Gen Fm

OA

57

(next page)

______ Rebecca

Wife

F

W

51

M

Y

Y

PA

PA

PA

Y

None

Thom Lucile

GDau

F

W

13

S

Y

Y

Y

PA

PA

PA

Y

None

Thom Robert

GSon

M

W

11

S

Y

Y

Y

PA

PA

PA

Y

None

*Little Valley

6.  1930 Census Every-Name-Index/Images (online at Ancestry.com, Image #6 of 14):  Penn Twp., Huntingdon Co., PA, Roll 2045, p. 3B, SN 3B, ED 31-36, SD 18, enumerated 14 Apr 1930, official enumeration date 1 Apr 1930 (extracted by Diana Gale Matthiesen):

1930:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

3

4

5

6

7

9

10

11

12

13

14

15

16

17

18

19

20

24

25

26

27

28

30

32

70

72

Corbin William J

Head

O

R

Y

M

W

70

Wd

N

Y

PA

PA

PA

Y

Farmer

Gen Farm

O

Y

N

46

Thom Clara J

Dau

F

W

43

Wd

N

Y

PA

PA

PA

Y

None

____ Robert W

GSon

M

W

21

S

N

Y

PA

PA

PA

Y

Laborer

Odd Jobs

W

Y

N

Ewing Ralph I

GSon-in-law

M

W

21

M

18

N

Y

PA

PA

PA

Y

Laborer

Odd Jobs

W

Y

N

_____ Lucille E

GDau

F

W

22

M

19

N

Y

PA

PA

PA

Y

None

7.  Anon.  12 Jun 1936.  "Obituary: William J. Corbin." Huntingdon Monitor, Huntingdon, PA (image online at Ancestry.com, attached to Public Member Trees; submitter, Jim Corbin; transcribed here by DGM):

WILLIAM J. CORBIN William J. Corbin, of Hesston, died at midnight last Friday, June 5th, following a complicated illness.  He was born in Huntingdon county on July 20, 1858, and was married to Miss Rebecca Isenberg, who has been dead for a number of years. These children survive him:  Harry Corbin, of Philadelphia; Mrs. Clara Thom. at home; Mrs. Ella Galbraith, of Huntingdon; and Mrs. Blanche Knode, of Marklesburg. Services were held at 2:30, Monday afternoon at the First Baptist church here, Rev. Paul Humphreys officiating, with burial in Riverview cemetery.

8.  James Corbin, photographer.  "Headstone: William J. CORBIN (1859-1936) & Rebecca I., His Wife (1868-1925)."  (image online at Ancestry.com, attached to Public Member Trees); submitter, Jim Corbin): Rebecca's middle initial here is clearly "I.," not "J.," and thus appears to stand for her maiden name, not her middle name.  She was fibbing about her age as she grew older, so the stone is apparently in error because, otherwise, she appears to have been born in 1858.

9.  Public Member Trees (online at Ancestry.com).

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