18 cities
| City | 2025 Pop. ↓ |
|---|---|
| Olbia | 60,261 |
| Orta di Atella | 24,750 |
| Oristano | 24,641 |
| Ostuni | 24,157 |
| Ottaviano | 23,396 |
| Orbassano | 21,813 |
| Orta Nova | 16,677 |
| Osimo | 16,610 |
| Oderzo | 15,764 |
| Omegna | 14,868 |
| Oria | 14,715 |
| Ospitaletto | 13,450 |
| Ortona | 13,327 |
| Oleggio | 12,655 |
| Olgiate Olona | 12,215 |
| Opera | 11,481 |
| Osio Sotto | 11,181 |
| Olgiate Comasco | 10,733 |