5 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Danbury | Western CT Planning Region | 89,341 |
| Darien | Western CT Planning Region | 22,866 |
| Derby | Naugatuck Valley Planning Region | 13,065 |
| Durham | Lower CT River Valley Planning Region | 7,237 |
| Deep River | Lower CT River Valley Planning Region | 4,498 |