Grolier was born in Lyon; he encouraged the belief that he was older than seems plausible given the marriage of his parents in 1485, resulting in 1479 often being given as his date of birth. Based on recently discovered documentary evidence from July 1527, when he gave his age as 37 in legal proceedings, he is now regarded as born in 1489-90. His family was of Italian origin, from Verona, but was based in Lyon where Étienne Grolier, Grolier's father, was a wealthy merchant who also held a government post as a tax collector. His mother was Antonia Esbauda; there were four daughters of the marriage, but Jean was their only son. In 1506 Étienne obtained, probably by purchase, the post of Treasurer-General of Milan, then held by the French. Jean Grolier was to inherit this office at the age of 19 or 20 on his father's death in Milan in 1509. Grolier still owned the family house in Lyons in 1536, though he had not lived there as an adult.