| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Middletown | 1 | 48,812 | 46,955 | 0.77% | 1,190 | 41 | City |
| Cromwell | 2 | 14,347 | 14,218 | -0.02% | 1,152 | 12 | Township |
| Clinton | 3 | 13,440 | 13,168 | 0.01% | 829 | 16 | Township |
| East Hampton | 4 | 13,192 | 12,689 | 0.44% | 370 | 36 | Township |
| Old Saybrook | 5 | 10,716 | 10,464 | 0.34% | 712 | 15 | Township |
| Portland | 6 | 9,445 | 9,365 | -0.04% | 404 | 23 | Township |
| Haddam | 7 | 9,106 | 8,440 | 1.78% | 207 | 44 | Township |
| East Haddam | 8 | 9,054 | 8,861 | 0.12% | 167 | 54 | Township |
| Old Lyme | 9 | 7,721 | 7,592 | 0.25% | 335 | 23 | Township |
| Durham | 10 | 7,201 | 7,143 | -0.11% | 304 | 24 | Township |
| Westbrook | 11 | 6,921 | 6,766 | 0.04% | 439 | 16 | Township |
| Essex | 12 | 6,818 | 6,726 | -0.01% | 655 | 10 | Township |
| Killingworth | 13 | 6,291 | 6,160 | 0.05% | 178 | 35 | Township |
| Deep River | 14 | 4,465 | 4,407 | -0.07% | 330 | 14 | Township |
| Middlefield | 15 | 4,286 | 4,212 | 0.23% | 339 | 13 | Township |
| Chester | 16 | 3,721 | 3,739 | -0.13% | 232 | 16 | Township |
| Lyme | 17 | 2,420 | 2,361 | -0.17% | 76 | 32 | Township |
Middletown is the largest city in Lower Connecticut River Valley Planning Region, with a population of 48,812.
Lyme is the smallest city in Lower Connecticut River Valley Planning Region, with a population of 2,420.
There are 17 cities in Lower Connecticut River Valley Planning Region, Connecticut.