21 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Waterbury | 1 | 116,412 | 113,889 | 0.43% | 4,076 | 29 | City |
| Bristol | 2 | 62,557 | 60,744 | 0.58% | 2,370 | 26 | City |
| Shelton | 3 | 43,315 | 40,762 | 1.19% | 1,414 | 31 | City |
| Naugatuck | 4 | 32,271 | 31,494 | 0.48% | 1,970 | 16 | Borough |
| Cheshire | 5 | 31,995 | 28,310 | 4.52% | 974 | 33 | Township |
| Watertown | 6 | 22,642 | 22,085 | 0.64% | 780 | 29 | Township |
| Southbury | 7 | 20,483 | 19,863 | 0.69% | 525 | 39 | Township |
| Ansonia | 8 | 19,269 | 18,896 | 0.39% | 3,201 | 6 | City |
| Seymour | 9 | 17,264 | 16,711 | 0.73% | 1,189 | 15 | Township |
| Wolcott | 10 | 16,625 | 16,131 | 0.69% | 816 | 20 | Township |
| Oxford | 11 | 13,354 | 12,711 | 0.68% | 408 | 33 | Township |
| Derby | 12 | 13,065 | 12,312 | 1.16% | 2,584 | 5 | City |
| Plymouth | 13 | 11,945 | 11,652 | 0.56% | 546 | 22 | Township |
| Woodbury | 14 | 10,027 | 9,712 | 0.67% | 276 | 36 | Township |
| Prospect | 15 | 9,629 | 9,374 | 0.58% | 678 | 14 | Township |
| Middlebury | 16 | 8,091 | 7,573 | 0.82% | 456 | 18 | Township |
| Thomaston | 17 | 7,600 | 7,439 | 0.45% | 634 | 12 | Township |
| Beacon Falls | 18 | 6,323 | 6,008 | 0.83% | 654 | 10 | Township |
| Watertown | 19 | 3,813 | 3,620 | 0.42% | 1,614 | 2 | CDP |
| Bethlehem | 20 | 3,463 | 3,389 | 0.41% | 179 | 19 | Township |
| Thomaston | 21 | 2,131 | 1,730 | 0.71% | 1,777 | 1 | CDP |
Waterbury is the largest city in Naugatuck Valley Planning Region, with a population of 116,412.
Thomaston is the smallest city in Naugatuck Valley Planning Region, with a population of 2,131.
There are 21 cities in Naugatuck Valley Planning Region, Connecticut.