From A Descriptive Work on Erie County, N.Y., Vol. II, Pub. 1898: Barnum, Theodore Downs, Buffalo, son of Stephen O. and Elizabeth (Chatfield) Barnum, was born in Utica, N.Y., April 23, 1842, and when an infant was brought by his parents to Buffalo, where his father has long been a prominent merchant and respected citizen. Mr. Barnum received his education in the Mount Vernon Boarding School and at Canandaigua Academy, and on the first call for troops in 1861 offered his services by helping to raise and organize a company of volunteers at Canandaigua. His place in this company, however, was filled and he promptly enlisted in Co. B, 74th N. Y. Regt., N. G., being chosen first lieutenant and afterward succeeding to the captaincy. On the call for troops at the first of the Gettysburg raid he went to the front with that regiment, and after serving on the field for some time he was ordered with his regiment to New York city to aid in quelling the draft riots. From there he returned to Buffalo and entered his father's store, in which he is now an active partner, the firm name being S. O. Barnum & Son. As a soldier and officer Captain Barnum served with much distinction, and as a business man he has achieved success and deserved popularity. Janr 21, 1864, he married Sarah, daughter of Rev. J. T. Avery of Cleveland, O., and their children are Fanny Elizabeth (Mrs. Langford S. Keating), Evelyn Avery and Stephana Ostrom.
From: Genealogical and family history of western New York: a record of the achievements of her people in the making of a commonwealth and the holding of a nation. William Richard Cutter, Lewis Historical Pub. Co., 1912, pages 520-521: Theodore Downs Barnum, so of Stephen Ostrom Barnum was born in Utica, NY on April 23, 1842 and died in Buffalo, NY in 1901. He was educated in the Buffalo schools and Canandaigua Military Academy. He served in the Civil War a captain of Company "C", 74th Regiment. Later he became associated with his father in business and on the death of the latter succeeded him, but only continued same one year after the latter’s death. He was a Republican and an elder of Westminster Presbyterian Church. He was a member of the Grand Army of the Republic and of the Buffalo Club. He married June 21, 1864, in Cleveland, Sarah Whitney, born 1843, daughter of Rev. John Thomas Whitney and Sarah Avery. Children: 1) Fanny Elizabeth, married first, April 8, 1891, Langford Spencer Keating, born in Buffalo, June 2, 1868, died May 31, 1899, child: Theodore Barnum Keating born January 5, 1894; married second April 28, 1903, James How of Buffalo, 2) Evelyn Avery born July 16, 1880 died November 1899; 3) Stephana Ostrom married Ralph H. Sidway.
From The New York Times, Dec. 2, 1900: Obituary Notes. Theodore D. Barnum, a prominent businessman of Buffalo, died Friday night. He was born at Utica in April, 1842.
He died without male issue.