| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Waterbury | 1 | 116,177 | 113,875 | 0.35% | 4,068 | 29 | City |
| Bristol | 2 | 62,686 | 60,744 | 0.55% | 2,375 | 26 | City |
| Shelton | 3 | 43,388 | 40,730 | 1.18% | 1,416 | 31 | City |
| Naugatuck | 4 | 32,380 | 31,496 | 0.47% | 1,976 | 16 | Borough |
| Cheshire | 5 | 31,393 | 28,292 | 1.32% | 956 | 33 | Township |
| Watertown | 6 | 22,574 | 22,082 | 0.21% | 778 | 29 | Township |
| Southbury | 7 | 20,597 | 19,860 | 0.63% | 528 | 39 | Township |
| Ansonia | 8 | 19,282 | 18,894 | 0.34% | 3,204 | 6 | City |
| Seymour | 9 | 17,196 | 16,713 | 0.25% | 1,184 | 15 | Township |
| Wolcott | 10 | 16,661 | 16,125 | 0.53% | 817 | 20 | Township |
| Oxford | 11 | 13,374 | 12,709 | 0.47% | 408 | 33 | Township |
| Derby | 12 | 13,071 | 12,311 | 1.13% | 2,585 | 5 | City |
| Plymouth | 13 | 11,941 | 11,652 | 0.33% | 546 | 22 | Township |
| Woodbury | 14 | 10,056 | 9,715 | 0.51% | 277 | 36 | Township |
| Prospect | 15 | 9,675 | 9,385 | 0.38% | 681 | 14 | Township |
| Middlebury | 16 | 8,165 | 7,579 | 0.89% | 460 | 18 | Township |
| Thomaston | 17 | 7,591 | 7,440 | 0.25% | 633 | 12 | Township |
| Beacon Falls | 18 | 6,341 | 6,007 | 0.54% | 655 | 10 | Township |
| Bethlehem | 19 | 3,468 | 3,384 | 0.38% | 179 | 19 | Township |
Waterbury is the largest city in Naugatuck Valley Planning Region, with a population of 116,177.
Bethlehem is the smallest city in Naugatuck Valley Planning Region, with a population of 3,468.
There are 19 cities in Naugatuck Valley Planning Region, Connecticut.