John G. Marsh was born in 1838, possibly in Ashland County, Ohio.
John left Ohio and moved west, eventually settling in Michigan and was probably living in Grand Rapids by the time the war broke out when he became a member of the Valley City Guard, the prewar Grand Rapids militia company whose members would form the nucleus of Company A.
He stood 6’0” with dark eyes, brown hair and a light complexion and was 23 years old and possibly living in Kent County when he enlisted in Company A on May 13, 1861. He was discharged for rheumatism on July 29, 1861, at Arlington Heights, Virginia.
It is not known if John returned to Michigan. In fact, after his discharge from the Third Michigan he may have returned to Ohio and was possibly the same John G. Marsh, age 25, who reentered the service as a Corporal in Company I, Twenty-ninth Ohio infantry, on October 29, 1861, and was mustered December 14. If so, he was promoted to First Sergeant, then to Second Lieutenant on December 12, 1862.
He was wounded on July 3, 1863, at Gettysburg, Pennsylvania, and subsequently died that same day. John was presumably one of the unknowns buried the Ohio plot, at the national cemetery in Gettysburg.
No pension seems to be available.