In ancient times, the village was indicated with the names of Susmano, Sosmano and Submano, toponyms perhaps deriving from the gens Sisimia, in the Todi land registry of 1322, it was described as a castle of "twenty-one fires" and was considered one of the many fortresses guarding the city of Todi; equipped with a fortified fortress dependent on the plebate of Santa Vittorina, it belonged to the noble Colas Jacobelli. In 1254 Sismano suffered great devastation by the militias of the Guelph league established in 1251 between Orvieto, Perugia, Spoleto, Narni and Florence against the Ghibellines of Todi and following this it remained for about a century lacking in defensive works. Between 1281 and 1294, Cardinal Benedetto Caetani spent long periods in Todi as mediator in the disputes between the league of the Guelph cities of Todi, Perugia and Spello and the Ghibelline city of Foligno.
In 1289, Cardinal Caetani had the opportunity to purchase, through the Florentine merchant Mainetto di Rinaldo dei Pulci, the castle of Sismano for 8500 gold florins. The Cardinal was able to often go to Sismano in the periods of suspension of the Conclave of Perugia in which Pietro del Morrone was made Pope, on 5 July 1294, with the name of Celestino V who, however, during the Consistory gathered in Naples, abdicated the 13 December of the same year. Nine days later, Cardinal Benedetto Caetani became Pope with the name of Boniface VIII. Still today on the sides of the fourteenth-century arch, which is located inside the Borgo, the two coats of arms of the Caetani can be admired, depicting two oblique waves on a shield. The Municipality of Todi had jurisdiction over Sismano until 1 December 1383 when Pope Urban VI ceded it to the Catalan Guelph Atti who died beheaded in 1393 in the Rocca di Orte, after being imprisoned by the Ghibelline Malatesta son of Pandolfo III Malatesta from Rimini. The wife of Catalano, at the head of an army, reconquered the castle in 1396. In 1462 it was occupied by Matteo di Ulisse Chiaravalle; In 1494 Ludovico and Giovanni I Atti returned to Todi with the help of the Baglioni, and hanged Matteo Chiaravalle's Onofrio in Sismano, whose relatives, in revenge, burned the village of Fiore, killing women and children. Alexander VI, tired of the continuous massacres between Atti and Chiaravalle, put an end to the disputes by gathering armies throughout Umbria that allowed the capture of Altobello Chiaravalle, later murdered by the angry mob in Acquasparta on 6 August 1500. In 1507 he had passed to Ludovico Acts which, after the death of Cesare Borgia with whom he had held important military posts, had become absolute lord of Todi; Ludovico, in 1503, with the help of Giampaolo Baglioni and Bartolomeo had razed the fortress of Todi to the ground. In 1528 Angelo Atti bought huge properties from Clement VII for 700 gold ducats; in 1563, Alessandro and Giovanni II, sons of Angelo, took over the property of Sismano together with Casigliano and Civitella del Lago. Eleonora Atti di Sismano married Orso II Orsini, a brutal and violent man so much so that in order to escape the abuses of her husband she was forced to hide . She took refuge in Morlupo, she was brought back to her consort who stabbed her to death (October 14, 1575). The news crossed the borders of Umbria: Orso II was forced to go to Florence to the Medici to justify himself, but he was not even received for his villainous gesture. The Acts were owners in alternating phases until the end of the 1500s. The coat of arms of the Atti is placed in the center of the second arch in the Borgo on the sides of which you can see the coats of arms of the Boniface VIII family. The properties of the Acts, following the massacre they ordered in Casigliano against the Cesi family, were confiscated by the Pope in the second half of the 16th century. On 10 April 1607, at the candle auction, the Florentine merchant Bartolommeo Corsini bought the fiefdom of Sismano for 97,000 scudi. Later the Corsinis were appointed by Pope Barberini, Urban VIII, princes of Sismano and this title is handed down from father to son to this day; the Corsinis, originally from Castelvecchio di Poggibonsi, gave the Church a pope, three cardinals and four bishops and other members of the family were ambassadors, ministers, imperial councilors, captains general of the papal troops and senators. Pio Tommaso Corsini, eighth prince of Sismano, participated in Italian political life by contributing as a deputy of the Constituent Assembly to the constitutional charter of the Italian Republic. Under the Corsinis, who restored what was left of the medieval castle by building a new wing in a purely seventeenth-century style, the fiefdom of Sismano became above all a large farm where, until the early 1960s, there were 32 farmhouses and had been inhabited for over 600 people who, for the most part, were linked to the farm by working relationships. Each family that lived in the farmhouse was committed to cultivating the fields, cutting wood, raising livestock, harvesting olives and grapes. The rows of vines were almost three meters high and were tied to trees, belonging to the elm family, called “stuccos” or “stiucci”; the pruning and harvesting were done with the stairs and the grapes were collected in wicker baskets that were carried on the shoulders with leather laces like a backpack.
In 2018 the Castello di Sismano was purchased together with 11 farmhouses and 580 hectares of land by the Societa 'Agricola Terre Del Papa Srl with the aim of redeveloping the historical and naturalistic heritage of the places and to produce High Quality Organic Extra Virgin Olive Oils. 'in total respect of Nature.