Jacob Cohn enlisted as a private in Company A, 54th Pennsylvania Infantry on February 10, 1864, during the American Civil War. He is listed among soldiers who served from Cambria County, Pennsylvania, in which Company A recruited. Cohn's name does not appear on the regiment's muster-out roll, and no further information about him could be found.

The 54th Pennsylvania Infantry was organized in Harrisburg, Pennsylvania in August and September, 1861, having recruited largely in Somerset and surrounding counties of southwestern Pennsylvania. In February 1862, the regiment was ordered to Washington, D. C., then to Harpers Ferry, (West) Virginia, from which the individual companies were dispatched to guard strategic points along a 60-mile section of the Baltimore & Ohio Railroad. Company A guarded the vicinity of South Branch Bridge.

As part of the Union Army's Department of West Virginia, the regiment participated in the Shenandoah Campaign of 1864, engaging the Confederates in several battles, including those at New Market, Piedmont and Lynchburg. In December 1864, the 54th was assigned to the Army of the James and transferred to Petersburg, Virginia. There, it participated in the siege against the city, the pursuit of Lee's forces, and the Appomattox campaign. The regiment was mustered out of service on July 15, 1865.