The Barnum Family, 1517-1904 says of him that he had four sons.
According to Veterans Administration records, William served as a private with the 2nd Independent Battery, Connecticut Light Artillery. His widow received a pension as an Army Widow.
From the Bridgeport Telegram of June 1, 1920: W. M. Barnum Dies on Memorial Day. William Marcus Barnum, veteran of the Civil War and assistant adjutant general and assistant quartermaster of the Grand Army of the republic of Connecticut died at his home 842 Lindley St., yesterday morning. He was 77 years of age. Over exertion in preparing for the annual Memorial services in this city hastened his end according to relatives. Had he lived he would have been one of the aides to Grand marshal Henry J. Seeley at the commemoration exercises yesterday Two weeks ago Adjutant General Barnum suffered an attack of acute indigestion. He made a quick recovery and despite the protestations of members of his family again resumed the arduous task of directing the activities of the Memorial Day committee, of which he was secretary. On last Wednesday he suffered a paralytic stroke and despite all that medical skill could do he succumbed yesterday morning, Funeral services will be held at 2 PM Wednesday afternoon at the late home. Rev. W. H. Day, pastor of the United Congregational Church will officiate. Burial will be in Union Cemetery, Stratford. His wife, Emma E. Barnum; four sons, Lewis S.,William M. Jr., Ernest E. and Arthur R., a daughter Mrs. H. B. Barnum of Stratford and a sister Mrs. William Sniffin survive him. Adjutant General Barnum was born in Stratford May 5, 1843. He enlisted in 1863 and was assigned to the Second Connecticut Light Artillery. He was but a short time in service when he was detached from his company and was stationed at General Grant’s headquarters where he did clerical work. Mr. Barnum was a fine penman and it was owing to this qualification that he was given such an important position. His stay in the army lasted but 11 months, as he was stricken by fever and after recuperation was given an honorable discharge. On his return home he engaged in the shirt making and cutting trade and worked at that occupation for 45 years. He was reputed to be an expert in that line and worked for a number of years in New York City. Since 1913 he was employed by the Barton Shirt company on Fairfield Avenue until five years ago, when he retired. In Grand Army circles, Adjutant General Barnum was most widely known. He served for five terms as Adjutant General of the Grand Army of the state and was past commander and adjutant of Elias Howe, No. 3 GAR of this city for several years. He always took an active interest in the local post and was ever ready at all times to assist the organization in its various undertakings.
Stratford was formerly known as Cupheag Plantation and prior to that Pequonnocke.