(a) John O'Brien was married on 21 May 1857 in a catholic church in Brooklyn, NY.  His marriage record that he was age 23, and from Mayo.  If his birthday occurred after that date, rather than before, he would have turned age 24 at that time.  This implies he was born either in 1833 or 1834.

(b) On 4 Jan 1864 he enlisted in the 173rd NY Infantry, stating that he was age 30.  Only 4 days into the year, it's highly likely that his birthday occurred after that date ... which means that he would turned age 31 after 4 Jan.  This implies he likely born in 1833.

(c) He was one of a number of soldiers captured in Louisiana the night of 9 Apr 1864, and was moved to Camp Ford at Tyler, TX, the largest Confederate prison camp west of the Mississippi River.  On 15 Sep 1864 he died of disease.

(d) John O'Brien left three children [a daughter and two sons] under the age of six. His oldest son [1861-1937] was less than three years of age when his father marched off to war - and he had no memories of his father.  

Additional Information
Date of Birth 1st Jan 1833 (circa)
Date of Death 15th Sep 1864

Some communities associated with this ancestor

Some ancestors associated with these communities

Some buildings associated with these communities

Some timeline events associated with this ancestor