16 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Killingly | 1 | 18,365 | 17,716 | 0.75% | 380 | 48 | Township |
| Plainfield | 2 | 15,513 | 14,974 | 0.64% | 366 | 42 | Township |
| Thompson | 3 | 9,743 | 9,192 | 1.19% | 208 | 47 | Township |
| Putnam | 4 | 9,561 | 9,218 | 0.81% | 471 | 20 | Township |
| Brooklyn | 5 | 8,862 | 8,382 | 0.88% | 304 | 29 | Township |
| Woodstock | 6 | 8,590 | 8,224 | 0.92% | 142 | 61 | Township |
| Canterbury | 7 | 5,368 | 5,048 | 1.38% | 134 | 40 | Township |
| Pomfret | 8 | 4,421 | 4,266 | 0.75% | 110 | 40 | Township |
| Ashford | 9 | 4,315 | 4,190 | 0.61% | 111 | 39 | Township |
| Sterling | 10 | 3,786 | 3,573 | 1.23% | 139 | 27 | Township |
| Voluntown | 11 | 2,714 | 2,568 | 1.19% | 70 | 39 | Township |
| Chaplin | 12 | 2,211 | 2,150 | 0.73% | 114 | 19 | Township |
| Hampton | 13 | 1,795 | 1,729 | 1.01% | 72 | 25 | Township |
| Eastford | 14 | 1,740 | 1,647 | 0.99% | 60 | 29 | Township |
| Scotland | 15 | 1,632 | 1,572 | 1.05% | 88 | 19 | Township |
| Union | 16 | 819 | 782 | 0.86% | 28 | 29 | Township |
Killingly is the largest city in Northeastern CT Planning Region, with a population of 18,365.
Union is the smallest city in Northeastern CT Planning Region, with a population of 819.
There are 16 cities in Northeastern CT Planning Region, Connecticut.