John Aaron Rawlins was born in 1831 in Guilford, Illinois. After working on the family farm, he moved to Galena, Illinois, where he studied the law, was admitted to the bar in 1855, and began a successful law practice.

During the Civil War, Rawlins joined the Union army and served throughout the conflict as the assistant-adjutant general heading General Ulysses S. Grant’s staff . Rawlins contracted tuberculosis, however, and by the time Grant was elected President in 1868, Rawlins was dying from the disease. Despite Rawlins’s condition -- indeed because of it -- Grant named Rawlins secretary of war, a post the dying man accepted but was unable to assume. General William Tecumseh Sherman served as acting secretary of war in all but name during much of Rawlins’s term. John Aaron Rawlins died in 1869.