The territory of Onano has ancient origins, dating back to prehistoric times, of which some findings testify.
Subsequently the area was first inhabited by the Umbrians and later by the Etruscans.
Even after the Roman occupation, the area remained undisturbed for a long time and the people who lived there gave birth to four groups of inhabitants, which over time became four villages. The union of these four villages created the first real town of Onano whose earliest records date back to the Medieval period.
Until the twelfth century P.C. in fact, we do not have definite informations about Onano. The only information we have is related to the fact that the districts of the village became part of the Lombard Tuscany, now owned fiefdom of Matilde di Canossa. In 1077 she then gave the territory to the Roman Church, along with many of her other possessions.
The first official news about Onano occurred around the twelfth century with a document in which it is reported that the village belonged to the Count Marcantonio Montemarte.
Onano was involved in the conflicts between Guelphs and Ghibellines, and for a time it also fell under the domain of Orvieto. From this moment on, the village was contested between the Umbrian Cities and the Papacy, because of its strategic position between Lazio and Tuscany.
Then the great noble families of the Monaldeschi and Sforza alternated each other, remaining in Onano throughout the Renaissance period.
The village was also property of the Sforza family in the sixteenth century, despite attempts by the Farnese to annex the Onano to their Duchy of Castro. However, in the seventeenth century it went back to the Church, to which it remained until in 1871 became part of the Kingdom of Italy.