北バージニア方面作戦
Subsequently, Stainrook was involved in organizing the 109th Pennsylvania Infantry and was commissioned its colonel with a nominal date of November 1, 1861. The regiment encamped in Philadelphia, Pennsylvania, near the State House before going to Virginia. His unit eventually became a part of the Army of Virginia under Maj. Gen. John Pope. Stainrook was wounded in the abdomen by a shell fragment at the Battle of Cedar Mountain during the Northern Virginia Campaign.