John G. O’Neill was born around 1841 in Ireland. He eventually immigrated to America, and by the early 1860s, he was probably living in Tennessee.

 

In April 1861, he received a commission as captain of Company A of the 10^th Tennessee Infantry. Union forces captured him at Fort Donelson in February 1862 and imprisoned him at Johnson’s Island. He was eventually exchanged, and he rejoined the regiment. The 10^th Tennessee took part in the Battle of Chickamauga and the Atlanta campaign.

 

He was promoted to major in May 1863 and to colonel in September 1864. He was wounded in the Battle of Resaca in May 1864. In October 1864, Confederate officials ordered him to enlist recruits from among Union prisoners in Georgia. He remained in the army until at least February 1865.

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