 Hacquet was mysterious about the time and place of his birth and the two have remained uncertain, although sources agree that he was an illegitimate child.Most sources have cited the information from his autobiography that he was born in 1739 or 1740 in Le Conquet, Brittany to an aristocratic father.When he lived in Ljubljana, he told Sigmund Zois that he was born to a Russian grandee, but this has not been supported by any sources.