| City | County | 2025 Pop. ↓ |
|---|---|---|
| Danbury | Western CT Planning Region | 86,385 |
| Darien | Western CT Planning Region | 22,218 |
| Derby | Naugatuck Valley Planning Region | 12,468 |
| Durham | Lower CT River Valley Planning Region | 7,200 |
| Deep River | Lower CT River Valley Planning Region | 4,474 |