Modern sources generally agree that Robert Prescott was born in Lancashire in 1726 or 1727. Some sources, such as the "Dictionary of Canadian Biography", claim that he was the son of a cavalry officer named Richard Prescott, though the "Oxford Dictionary of National Biography" says that "on what grounds [this] is not clear." Other sources also suggest that he was the brother of Colonel William Prescott, who fought in some of the same conflicts, although William Prescott was an American who was born in Massachusetts. Older sources differ from modern ones in some respects, with the 1896 "Dictionary of National Biography" and the 1900 "Appletons' Cyclopædia of American Biography" both claiming that he was born in 1725; the "Dictionary of National Biography" further states that "his family lost their estates owing to their opposition to the revolution of 1688."