John Randolph Vaill was the son of Cornwall shoemaker Philander Vaill and Urena (Johnson) Vaill. His brother George Washington Vaill served in the 1st C.H.A.; brother Henry Lyman Vaill served in the Second Heavy Artillery and died in 1864.

John Vaill died of typhoid fever in the hospital at Hilton Head, South Carolina on July 5, 1862 and was buried at Beaufort National Cemetery.