| Zip Code | City | Population ↓ |
|---|---|---|
| 06360 | Norwich | 37,216 |
| 06340 | Groton | 29,863 |
| 06320 | New London | 27,703 |
| 06226 | Willimantic | 19,344 |
| 06415 | Colchester | 16,038 |
| 06385 | Waterford | 15,966 |
| 06351 | Jewett City | 15,760 |
| 06355 | Mystic | 12,173 |
| 06357 | Niantic | 11,332 |
| 06382 | Uncasville | 10,143 |
| 06339 | Ledyard | 9,113 |
| 06379 | Pawcatuck | 9,017 |
| 06333 | East Lyme | 7,389 |
| 06370 | Oakdale | 7,327 |
| 06249 | Lebanon | 7,116 |
| 06335 | Gales Ferry | 6,307 |
| 06378 | Stonington | 5,555 |
| 06359 | North Stonington | 5,160 |
| 06365 | Preston | 4,807 |
| 06420 | Salem | 4,368 |
| 06375 | Quaker Hill | 3,670 |
| 06330 | Baltic | 3,327 |
| 06280 | Windham | 3,110 |
| 06380 | Taftville | 2,757 |
| 06334 | Bozrah | 2,249 |
| 06254 | North Franklin | 2,004 |
| 06256 | North Windham | 1,704 |
| 06353 | Montville | 439 |
| 06266 | South Windham | 222 |
| 06350 | Hanover | 121 |
| 06336 | Gilman | 44 |
| 06338 | Mashantucket | 27 |
| 06389 | Yantic | 0 |
The data shown reflect ZCTAs from the US Census. As of 2025, there are 33 ZCTAs in Southeastern Connecticut Planning Region, Connecticut (US Census).