The Barnum Family, 1350-1907 shows considerable confusion about this individual. That source has him born 9 Aug 1840 (although his father was born in 1743) and married to Bersheba Piseley. Other sources show a Beersheba Pixley married to Alanson Levi Barnum, third cousin once removed of David Barnum. Because of that confusion, the death date of 22 May 1846 given here must also be viewed with caution.
David was born in Danbury and moved to Kent with his father in 1752, thus becoming one of its early settlers. He had seven children, Ebenezer, Delilah, Abigail, Lydia, Sylvester, David and John, all born in Kent. In 1811 he moved to New York.