Petritoli was founded by Farfensi monks in the 10th century with the name of Castel Rodolfo. Passed under Transaric baron of Saltareccia, it was given to the bishop of Fermo in 1055. Since 1198, it had its own government until Frederick II conquested it in 1250, and then ceded it to Fermo again, an imperial ally. After various events, which saw sieges and destruction, alternated periods of relative autonomy with periods of submission to Fermo. At Napoleon times, Petritoli got the title of Canton, actively participating in the subsequent uprisings of Risorgimento.
The name Petritoli would derive from the merger of the three castles of Petrosa, Petrania, and Petrollavia, but the etymology is controversial, as these names refer to three villages, and related streets, built outside the castle walls.

Through three pointed arches from the nineteenth-century, and two fifteenth-century towers, you enter the ancient town.
The former convent of the Poor Clares, now Palazzo Comunale, preserves a seventeenth-century wooden choir in an interior room.
The Civic Tower was built in the nineteenth century by superimposing three different plans: a square ashlar base, an octagonal body above and a round terminal crowned by a small dome, both in brick masonry. In the main street is the twentieth-century Palazzo Vitali, in Venetian-Gothic style. Next door is the Teatro dell’Iride (1873–77), built to a design by Giuseppe Sabbatini.
Outside the old town, there is the former convent of the Minori Osservanti, now used as a clinic, the adjoining church, with an eighteenth-century ceiling with octagonal coffered decorated with egg yolk tempera, preserves an organ by Callido inside. < br> The hamlet of Moregnano, a Municipality until 1869, is structured as a fortified settlement; while the Valmir hamlet is located along the Val d’Aso state road 433.