The Genealogical Record of the Barnum Family mistakenly shows him as the son of Stephen Barnum and Lucy Wolcott, while The Barnum Family, 1517-1904 correctly shows him as a child of Stephen's marriage to his second wife, Ruth North. An error in The Barnum Family, 1350-1907 mistakenly truncates the line with Roswell's grandfather Jabez, providing no information for the succeeding generations.
In the 1830 US Census for Shoreham, Addison, Vermont the family of Roswell Barnum is enumerated as follows: Males 5-10, one (probably John, thus born 1820-1825); Males 20 to 30, one (Roswell, thus born 1800-1810); Females under 5, three (Tryphena Matilda, Sophrona and Jennette, thus all born 1825-1830); Females 20-30 (Tryphena Glidden, thus born 1800-1810).
Other Barnum families enumerated in Shoreham in the same census were those of Stephen, Orrin and Medad Barnum. They were certainly three of his half brothers, sons of his father Deacon Stephen Barnum by his by first wife Lucy Wright Wolcott.