John D. O’Neil was born in 1836.
John was 25 years old and probably living in Detroit, Michigan, when he enlisted in Company K on May 13, 1861. He was reported as a provost guard in July of 1862, a provost guard at Brigade headquarters from August of 1862 through February of 1863, on detached service with the ambulance train in October of 1863 through May of 1864, and was mustered out on June 20, 1864, at Detroit.
John was probably living in Detroit when he was admitted on December 6, 1873, to Harper Hospital in Detroit (the predecessor to the Michigan Soldiers’ Home hospital) for “inflammation of the brain,” and he died at the hospital on December 22, 1873. He was presumably buried in Detroit.
No pension seems to be available.