John William Hendrix was born around 1842 in New York to Stephen and Hannah Hendrix. His father was a farmer who owned $2,000 of real estate and $200 of personal property by 1860. He grew up in Otego, New York, and by 1860, he was working as a farm laborer.
He enlisted in the Union army on October 5, 1861, and he mustered in as a private in Company E of the 90th New York Infantry on October 28. He died of disease in Key West, Florida, on September 4, 1862.