Cyrus Pettijohn was born around 1834 in Ohio to Sarah J. Pettijohn. His father died by the early 1840s, and his mother married Peter Cornetet in 1844. The family lived in White Oak, Ohio, and his stepfather was a miller who owned $900 of real estate by 1850.
He enlisted in the Union army on August 12, 1862, and he mustered in as a private in Company E of the 50th Ohio Infantry two weeks later. The regiment took part in the Battle of Perryville, the Atlanta campaign, and the Carolinas campaign. He was wounded near Dallas, Georgia, on May 31, 1864, and surgeons amputated his left arm. He apparently rejoined the regiment in August 1864, and Confederate forces captured him in the Battle of Franklin on November 30, 1864. He was eventually exchanged, and he rejoined the regiment. He died in the Sultana explosion on April 27, 1865.