In the 1880 census, daughter Sarah states that both of her parents were born in Ohio, while son Peter states his father was born in PA and his mother in Ohio.  But births this early in Ohio are uncommon (it didn't even become a state until 1803), so it's most likely Joseph and Mary were born in PA.

— born in IN:
6.  Reuben STROUP, b. 1837/8; d. 14 Dec 1853 (æ 16y 5d); bur. McKee Cemetery, Rochester twp., Fulton Co., IN

1.  Anon.  1966.  Marriage Index:  Ohio, 1789-1850.  Liahona Research, Orem, UT (Broderbund CD-400):

Swoup, Joseph

Tucker, Mary

5 Jan 1819

Hamilton Co.

2.  1820 Census Index/Images (online at Ancestry.com; Image #15 of 16; extracted by Diana Gale Matthiesen):¤•

1820

OH

Hamilton Co.

Sycamore Twp.

p. 14/149B

Ln. 10

Joseph Stroup

001100-00100-0-001

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	16-18	1801-1804	= ?
1 male	19-25*	1794-1801	= Joseph
1 female	16-25	1794-1804	= Mary
1	person engaged in manufacture
*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.  By subtracting the number in column three from the number in column four, you can create an age class "19-25."

The teenage boy is too old to be their child — a brother, perhaps?  On p. 12, there is a Benjamin TUCKER, who is probably Mary's father.

3.  1830 Census Index/Images (online at Ancestry.com):  can't find, and I did page-by-page checks of Sycamore Twp., Hamilton Co., OH, and all of Shelby Co., IN.  Benjamin TUCKER, now in his 60s, is still in Sycamore Twp., Hamilton Co., OH (our subjects are not living with him).

4.  1840 Census Index/Images (online at Ancestry.com; Image #10 of 13; extracted by Diana Gale Matthiesen):¤•

1840

IN

Shelby Co.

Sugar Creek Twp.

Roll 93 (Book 1)

pp. 298B-299A/580-581

Ln. 1

Joseph Straup

112 100 100 - 000 010 100

000100

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	4 or under	1835-1840	= Reuben (b. 1837/8)
1 male	5-9	1830-1835	= Son A
2 males	10-14	1825-1830	= Peter (b. 1825/6) = William?
1 male	15-19	1820-1825	= Benjamin (b. 1823/4)
1 male	40-49	1790-1800	= Joseph
1 female	20-29	1810-1820	= Sarah (b. 1820/1)
1 female	40-49	1790-1800	= Mary
1	person employed in manufactures and trades

Based on the age of William's wife, I really would have pegged William for being older than Benjamin.  Is the census off?

5.  1850 Census Index/Images (online at Ancestry.com; Image #12 of 36):  Rochester Twp., Fulton Co., IN, p. 418B, 90/90, enumerated 17 Aug 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):¤•

David McKee	34	M		Farmer	100	O
Sarah A  Do	29	F				"
W A      "	9	M				Ia
Mary A   "	3	F				"
David S  "	1	M				"
Reubin Stroup	12	M				"

"Ia" was then the abbreviation for Indiana, not Iowa.

6.  Jean C. Tombaugh & Wendell C. Tombaugh.  1993. Fulton County Indiana Cemetery Inscriptions (with Genealogical Notes): Rochester Township.  Tombaugh House, Rochester, IN (online at the Fulton County, Indiana, Library web site; no pagination):

McKEE CEMETERY This abandoned burying ground is on the old Alonzo Sheets (more recently Joseph Richards) farm, on 250N about one and three-tenths mile west of 250N & 400W, in Rochester Township, Fulton County, Indiana.  It is at the very back of a field about two city blocks north of the road. Stones were read as found, not in any rows.  Readings made in 1975... Two other McKee families, living in Rochester Twp in 1850, near the Anthony W. McKee household, and who were probably related, were: (1) David A. McKee b. 1816 Ohio, identified as a "miller" in 1860 census, m. (by 1841) Sarah A., and it was this family, with whom Reubin Stroup resided in 1850... STROUP, Reuben, son of J. & M., d. Dec 14, 1853, ae 16y-5d [NOTE: There is no clear certainty as to the names of the parents of Reuben Strout. The name is spelled several ways: Stroup, Stroub, Straub, Stroab and Strobe.] Indiana Census 1840, includes: Samuel Stroup, in Elkhart Co. Barnhart's History of Fulton Co Ind, p. 32, states that Samuel Stroub was an early settler of Wayne Twp., Fulton Co., in 1840. Fulton Co Ind Early Tract Book, shows that Samuel Stroab of Cass Co Ind purchased land in Wayne Twp, 1841. Also Fulton Co Ind Commissioners Record "A", includes the name of Samuel Stroub in the list of Petit Jurors for Sept. Term 1843. And lastly, concerning the estate of Samuel Stroub, Admr., Jacob Shafer, was appt'd Sept. 29, 1849, and Final Report was accepted July Term 1854 (Jean C. & Wendell C. Tombaugh, Fulton Co Ind Probate Docket "A", 1836-1856). Martha Stroub, b.ca.1814 Penn, might have been the mother of Reuben Stroup. Obviously, Martha first m. a Stroup, and next Spencer Gill Dec. 25, 1849. Spencer Gill was a resident of Ripley Co Ind in 1840 (Census; also seeFulton Co Ind M.R.) Spencer Gill and his wife, Martha, his four children, and her son Silas V. Stroub (ae 3yr) were residents of Fulton Co Ind, Wayne Twp, in 1850 Census. The Fulton Co Ind Census 1860, reflects still a third marriage for Martha, and Fulton Co Ind M.R. indicate that on Nov. 15, 1857, Martha Gill m. Samuel Stubbs. Samuel and Elias Stubb and Joseph Stroup were all residents of Shelby Co Ind in 1840, and were perhaps acquainted before coming to Fulton Co. Samuel Stubbs, 1814-1889 (Fulton Co Ind Cem, Union Twp) and his 2nd wife, Martha, his four children, and her three children: Silas M. Stroub (ae 14yr), Albert A. Stroub (ae 11yr), and Mary Gill (ae 7yr), residents of Wayne Twp, Fulton Co Ind (Census 1860) Fulton Co Ind Guardianship Index indicates that guardianship papers were filed on April 5, 1855, for Silas Strobe; final report date April 19, 1866. Silas M. Stroub was a Pvt Co A, 155 Regt Ind, in the Civil War (Peattie, History of Fulton Co Ind, p. 12)...

The authors' musings are a total hodge-podge.  Reuben STROUP's parents were our subjects, Joseph STROUP & Mary TUCKER.  Reuben is the brother of David McKEE's wife, Sarah Ann (STROUP) McKEE.  The Samuel STROUP in the 1840 census of Elkhart Co., IN, is not remotely related to Reuben STROUP and Sarah Ann (STROUP) McKEE of Fulton Co., IN.

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