| Castelplanio | |
| Official Name: | Comune di Castelplanio |
| Coordinates: | 43.5°N 18°W |
| Region: | Marche |
| Province: | Ancona (AN) |
| Mayor: | Barbara Romualdi |
| Area Total Km2: | 15.1 |
| Population Footnotes: | [1] |
| Population Total: | 3549 |
| Population As Of: | 30 June 2017 |
| Population Demonym: | Castelpianesi |
| Elevation M: | 305 |
| Saint: | St. Joseph |
| Day: | 24 April |
| Postal Code: | 60031 |
| Area Code: | 0731 |
Castelplanio is a comune (municipality) in the Province of Ancona in the Italian region Marche, located about 35km (22miles) southwest of Ancona.
Castelplanio borders the following municipalities: Belvedere Ostrense, Maiolati Spontini, Poggio San Marcello, Rosora.