6 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Oxford town | Worcester County | 13,276 |
| Orange town | Franklin County | 7,536 |
| Orleans town | Barnstable County | 6,323 |
| Oak Bluffs town | Dukes County | 5,265 |
| Oakham town | Worcester County | 1,930 |
| Otis town | Berkshire County | 1,599 |