In 1931, the Prussian scholar E. Möller discovered in a notarial deed from Vinci an annotation concerning the birth and baptism of Leonardo. The note, entered by his grandfather Antonio di Piero da Vinci, on a document dated 1452, that had belonged to his own father, a notary by profession, confutes the hypothesis that Leonardo was born at Anchiano, a village a few kilometers from Vinci, as had been thought until then. Antonio da Vinci wrote: «My grandson was born, son of Ser Piero my son, on the day of April 15, a Saturday, at the hour of three in the night. He was named Lionardo. The priest Piero di Bartolomeo da Vinci baptised him […].» These words are followed by a long list of persons whose identity was unquestionably linked to the town of Vinci, where Leonardo's family, although having obtained Florentine citizenship in the 14th century, had kept its residence.

Of Leonardo's father, Ser Piero, it is known that he entered the profession of notary in 1448, residing permanently in Florence and making regular visits to Pisa.

A second document coming from Ser Antonio provides further information on Leonardo's mother and his illegitimate birth. In the Land Office report of 1458, Ser Antonio counts among the members of his family, «Lionardo son of the said Ser Piero, not legitimate, born of him and Chateri[n]a, now the woman of Achattabriga di Piero Del Vaccha da Vinci since 5 years.»

Apart from the name and identity of the man she had married after the birth of her child, nothing else is known of Leonardo's mother. Presumably, she was a girl of humble origin, as suggested by the fact that no marriage with Ser Piero was taken into consideration, and she was given as bride to a simple "fornaciaio", a worker in the kilns.

The choice of the name with which Leonardo was baptised, not a traditional family name, suggests that starting from his baptism there was never any intention of legitimizing the child. Nonetheless, he seems to have spent his childhood at Vinci, with his father's family. Being an illegitimate son, however, he could not have become a notary nor enjoyed the benefits of citizenship, nor make any claim to the family property without explicit legal authorization to do so. Among the family members, it seems that the figure closest to Leonardo in his childhood was probably his uncle Francesco, Ser Piero's brother, who named him as heir in his will.

It is known for certain that Leonardo remained with his family at least up to 1469, the time of the last Land Office report in which he is listed among the dependents of his grandfather Antonio. In the next census, in 1480, he is not included among the members of his paternal family; it is thus assumed that he must have already left Vinci by that date.