Cesio is an Italian surname of toponymic type, derived from the name of the comune of Cesio (in Ligurian Cêxi), a small locality of approximately 260 inhabitants in the province of Imperia (Liguria). It is situated in the upper valley of the Impero torrent, on the old road towards the Nava pass, on the border with the Arroscia valley.

The place name is documented in medieval sources from the 14th century, where it appears as Cezio in references of a residential character, as in the case of Facitus Ferrerius de Cezio (1346). However, its origin seems even older, since it can be related to the form Céxeno, mentioned in a document of 1150 relating to the tithes of the territory of the Maro valley.

The etymology of Cesio is disputed and admits several hypotheses. The first links it with the Roman gentilic nomen Caesius, belonging to a Roman gens related to the cognomen Caesar, traditionally associated both with the Latin verb caedere ("to cut") and, according to an old legendary tradition, with the birth by caesarean section of the first member of the family. Within this line of interpretation, the surname is connected with the onomastic group of Cesi and Cesini, documented by Rossoni as derived from the Latin gens Cesia. The same author notes as a possible original nucleus the place name Cesi, an Umbrian castle from which Pietro Cesi, considered the founder of the lineage of the homonymous noble family, would have come.

A second hypothesis proposes that Cesio is a place name of uncertain origin, possibly an old name of property or settlement whose original form cannot be clearly reconstructed or linked to a recognisable suffix or etymological structure. In this sense, the name would have evolved autonomously over time, preserving only a fossilised form in the current toponymy.

Finally, a third reading relates it to a possible apocope of the place name Concesio (province of Brescia), although this interpretation is less accepted.

As for its distribution, the surname is concentrated mainly in Liguria, especially in the Imperia area, with minor presences in Umbria and Lombardy.