| Cassano all'Ionio | |
| Official Name: | Comune di Cassano all'Ionio |
| Coordinates: | 39.7833°N 35°W |
| Region: | Calabria |
| Province: | Cosenza (CS) |
| Frazioni: | Doria, Lauropoli, Sibari |
| Mayor: | None (commissars) |
| Area Total Km2: | 159.07 |
| Population Total: | 18652 |
| Population As Of: | December 2013 |
| Population Demonym: | Cassanesi |
| Elevation M: | 250 |
| Saint: | Holy Crucifix |
| Day: | First Friday in March |
| Postal Code: | 87011 |
| Area Code: | 0981 |
Cassano all'Ionio, also named Cassano allo Ionio, is a town and comune in the province of Cosenza in Calabria, southern Italy, known in Roman times as Cassanum. It lies in a fertile region in the concave recess of a steep mountain, 60 km northeast of the town of Cosenza, 10 km west of the archaeological site of Sybaris.
Cassano was the site of great Saracen defeat of the Byzantine forces in Italy under Pothos in 1031.
The diocese of Cassano was first mentioned in 1059.
The rock above the city is crowned by a medieval castle commanding beautiful views. Its tower was believed to be that from which the stone was thrown that killed Milo, but that may be due to an erroneous identification of the town. There are warm sulfurous springs here, which have been used for baths.
The archaeological site of Sybaris, located near the modern town of Sibari, is part of the comune of Cassano allo Ionio.