Individual Details

I found two possible marriages for George in Vigo County.
George M. Harrison to Frances Lowe, 2 Jan 1871
George M. Harrison to Frances Harrison, 1 Dec 1881 [was this possibly a remarriage?]
He was noted as having been married, but his wife deceased, when he was at the Home for Disabled Volunteer Soldiers.

1880 Census. Harrison Twp, Vigo, IN
List of inmates of the Vigo county poor asylum - George was listed last after the superintendent, his sister, and a servant.
George M. Harrison, 42, divorced, had hernia, b. IN, father b. NY, mother b. NY

US National Homes for Disabled Volunteer Soldiers, 1866-1938; FamilySearch.org
George M. Harrison
Enlisted 20 Sep 1861 at Mattoon, Illinois
1st Lt, Co B. 7th Illinois Infantry
Discharged 9 Jul 1865, Corinth, Mississippi - Served until close of war
Disability due to Double Hernia, contracted Jun 1862 in Corinth, MI
Born in Indiana, age 56, blue eyes, light hair, can read & write, Protestent, Laborer by occupation
Residence after discharge: Terre Haute, IN
Widower
Near Relative: Fernando Harrison, Govt. Printing Office, Washington, DC
Pension: $15. Admitted M. B. 17 Aug 1894 (this makes his birth year 1838)
Died M. B. Hospital 13 March 1895 of Apoplexy
Pension Certificate #194.807
Personal Effects Appraised at $2.20.
Buried Grave No. 190 - Circle 2
Note: I believe M. B. stood for the Marion Brach, Marion, Grant Co, Indiana.

http://www.ingenweb.org/ingrant/SDW/vahosp.htm
'up the Mississinewa probably ten miles is the resting place of other
of the Nation's Heroes. Established by an act of Congress July 23, 1888
and given the name of Marion Branch National Military Home, Indiana. Plans
for the establishing of this hospital were consummated in 1890. A burial
ground was set aside at some distance from the buildings which we for years
have called "THE HOME". Here Governor Campbell, first Governor of the home,
planned "The Silent Circle". Number 1 in this plat is Thomas Jefferson,
Co. B 2nd N.Y. Cav., number 1345 is John W. Stewart Indiana Serg't 9 Cav.
This Silent Circle is designated as Section 1. The numbers are in
succession but do not indicate the order of death. A section has been
reserved in this part for the burial of civilian employees and members of
officer's families. All others who are buried in this cemetery are those
who have participated in Military Services of the United States and who have
received honorable discharge.

The cemetery is online from this website - however, George M. Harrison's grave not found.
However, FindAGrave #55279038 has a picture of his marker in the Marion National Cemetery. G. M. Harrison. He died 13 March 1895 and served as a Lieutenant in Company B, 7th Illinois Infantry. He is shown in Section 1, Row 2, Plot 180 (not 190).

Birth	1838	Indiana
Death	13 Mar 1895	Marion, Grant County, Indiana

Father	Brittain Moore Harrison (1801 - 1873)
Mother	Adaline Allen (1814 - 1857)
Sibling	Dennis Allen Harrison (1830 - 1892)
Sibling	Ann Elizabeth Harrison (1834 - )
Sibling	Mary Allen Harrison (1840 - 1871)
Sibling	Albert B. Harrison (1842 - )
Sibling	Augustus Porter Harrison (1848 - 1915)
Sibling	Fred Harrison (1853 - )