| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Killingly | 1 | 18,281 | 17,684 | 0.57% | 378 | 48 | Township |
| Plainfield | 2 | 15,432 | 14,994 | 0.33% | 364 | 42 | Township |
| Thompson | 3 | 9,647 | 9,184 | 0.85% | 206 | 47 | Township |
| Putnam | 4 | 9,424 | 9,216 | 0.23% | 464 | 20 | Township |
| Brooklyn | 5 | 8,791 | 8,391 | 0.49% | 302 | 29 | Township |
| Woodstock | 6 | 8,502 | 8,228 | 0.33% | 140 | 61 | Township |
| Canterbury | 7 | 5,289 | 5,039 | 0.72% | 132 | 40 | Township |
| Pomfret | 8 | 4,400 | 4,269 | 0.5% | 109 | 40 | Township |
| Ashford | 9 | 4,275 | 4,188 | 0.23% | 110 | 39 | Township |
| Sterling | 10 | 3,763 | 3,581 | 0.72% | 138 | 27 | Township |
| Voluntown | 11 | 2,661 | 2,563 | 0.3% | 68 | 39 | Township |
| Chaplin | 12 | 2,196 | 2,148 | 0.41% | 113 | 19 | Township |
| Hampton | 13 | 1,778 | 1,732 | 0.57% | 71 | 25 | Township |
| Eastford | 14 | 1,727 | 1,648 | 0.7% | 60 | 29 | Township |
| Scotland | 15 | 1,596 | 1,564 | 0.31% | 86 | 19 | Township |
| Union | 16 | 803 | 783 | -0.12% | 28 | 29 | Township |
Killingly is the largest city in Northeastern Connecticut Planning Region, with a population of 18,281.
Union is the smallest city in Northeastern Connecticut Planning Region, with a population of 803.
There are 16 cities in Northeastern Connecticut Planning Region, Connecticut.