| Zip Code | City | Population ↓ |
|---|---|---|
| 06457 | Middletown | 46,720 |
| 06416 | Cromwell | 14,334 |
| 06413 | Clinton | 13,377 |
| 06424 | East Hampton | 12,751 |
| 06475 | Old Saybrook | 10,575 |
| 06371 | Old Lyme | 9,828 |
| 06480 | Portland | 9,434 |
| 06422 | Durham | 7,208 |
| 06498 | Westbrook | 6,856 |
| 06419 | Killingworth | 6,240 |
| 06441 | Higganum | 5,348 |
| 06423 | East Haddam | 5,182 |
| 06417 | Deep River | 4,458 |
| 06412 | Chester | 3,825 |
| 06469 | Moodus | 3,311 |
| 06426 | Essex | 3,267 |
| 06438 | Haddam | 2,887 |
| 06442 | Ivoryton | 2,826 |
| 06455 | Middlefield | 2,480 |
| 06481 | Rockfall | 1,763 |
| 06459 | Middletown | 1,238 |
| 06409 | Centerbrook | 701 |
| 06414 | Cobalt | 302 |
| 06456 | Middle Haddam | 281 |
| 06376 | South Lyme | 89 |
| 06439 | Hadlyme | 65 |
The data shown reflect ZCTAs from the US Census. As of 2025, there are 26 ZCTAs in Lower Connecticut River Valley Planning Region, Connecticut (US Census).