12 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Odenton | Anne Arundel County | 46,885 |
| Owings Mills | Baltimore County | 36,396 |
| Olney | Montgomery County | 36,332 |
| Oxon Hill | Prince George's County | 18,609 |
| Overlea | Baltimore County | 12,454 |
| Ocean Pines | Worcester County | 12,077 |
| Ocean City | Worcester County | 6,892 |
| Owings | Calvert County | 2,525 |
| Oakland | Garrett County | 1,805 |
| Oxford | Talbot County | 599 |
| Oldtown | Allegany County | 87 |
| Ocean | Allegany County | 12 |