During the Civil War, Fort Mifflin was used to house Confederate prisoners of war, as well as Union soldiers and civilians accused of breaking the law. On November 24, 1864, LTC Seth Eastman, the great American Western frontier painter, was sent to Ft. Mifflin to supervise the discharge all of the over 200 civilian and military prisoners. On January 2 1865, Eastman reported his garrison consisted of B Company, 186th PA Vol, a detachment of recruits and the hospital staff. On August 20 1865, Eastman was relieved by CPT Thomas E. Merritt, with A Company, 7th US Veteran volunteers.