James Hervey Simpson was an officer in the U.S. Army and a member of the United States Corps of Topographical Engineers.

During the American Civil War, Simpson served as colonel of the 4th New Jersey Volunteer Infantry and was captured at the Battle of Gaines's Mill. He was paroled and returned, but resigned his commission of volunteers on August 24, 1862 to return to his rank of major in the Corps of Topographical Engineers. He was attached to the Department of the Ohio and was in charge of the expansion and improvements of the defenses for Cincinnati, Ohio. For his services during the war, Simpson was brevetted to the rank of brigadier general.