17 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Middletown | 1 | 49,436 | 46,976 | 0.84% | 1,205 | 41 | City |
| Cromwell | 2 | 14,416 | 14,214 | 0.1% | 1,158 | 12 | Township |
| Clinton | 3 | 13,503 | 13,173 | 0.13% | 833 | 16 | Township |
| East Hampton | 4 | 13,275 | 12,697 | 0.63% | 372 | 36 | Township |
| Old Saybrook | 5 | 10,823 | 10,468 | 0.62% | 719 | 15 | Township |
| Portland | 6 | 9,528 | 9,361 | 0.26% | 408 | 23 | Township |
| East Haddam | 7 | 9,151 | 8,858 | 0.49% | 169 | 54 | Township |
| Haddam | 8 | 8,824 | 8,437 | 0.1% | 201 | 44 | Township |
| Old Lyme | 9 | 7,745 | 7,604 | 0.16% | 337 | 23 | Township |
| Durham | 10 | 7,244 | 7,141 | 0.1% | 306 | 24 | Township |
| Westbrook | 11 | 6,950 | 6,761 | 0.23% | 441 | 16 | Township |
| Essex | 12 | 6,873 | 6,728 | 0.19% | 661 | 10 | Township |
| Killingworth | 13 | 6,312 | 6,162 | 0.22% | 179 | 35 | Township |
| Deep River | 14 | 4,513 | 4,405 | 0.33% | 334 | 14 | Township |
| Middlefield | 15 | 4,288 | 4,208 | 0.16% | 339 | 13 | Township |
| Chester | 16 | 3,756 | 3,739 | 0.11% | 234 | 16 | Township |
| Lyme | 17 | 2,429 | 2,349 | 0.16% | 76 | 32 | Township |
Middletown is the largest city in Lower CT River Valley Planning Region, with a population of 49,436.
Lyme is the smallest city in Lower CT River Valley Planning Region, with a population of 2,429.
There are 17 cities in Lower CT River Valley Planning Region, Connecticut.