The surname Molyneaux also appears in the historic record as Molynex, Molineaux and Mullinex, among others. ''The Barnum Family, 1517-1904'' mentions Sarah Williams as the wife of Bethuel Barnum, while the 1907 edition of that work lists no wife for Bethuel. The ''Genealogical Record of the Barnum Family'' shows her as Sarah Molynex. The mention of Sarah Wiliams might refer to another wife, or simply be an error. Sarah was probably born in Dutchess County, New York. Her mother was probably Charity Baxter, and her grandmother may have been Abigail Clinton.
Two different possible birth years have been found for Sarah; about 1760 and about 1775. Neither is supported by valid, verifiable source citations. If we are to accept the year 1775, she would have been 16 years old when her first child was born. Although possible, it's unlikely for the times, when most marriages occurred during the mid-20s of the wife. The birth year of about 1760 seems more logical since it would have made her 31 at the birth of her first child.