| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Greater Bridgeport Planning Region | 1 | 4.82% | 340,032 | 324,397 |
| Western CT Planning Region | 2 | 4.05% | 643,825 | 618,762 |
| Naugatuck Valley Planning Region | 3 | 3.96% | 466,831 | 449,055 |
| Capitol Planning Region | 4 | 3.69% | 999,690 | 964,088 |
| Northeastern CT Planning Region | 5 | 3.5% | 98,568 | 95,231 |
| Lower CT River Valley Planning Region | 6 | 2.96% | 178,406 | 173,281 |
| South Central CT Planning Region | 7 | 2.83% | 580,517 | 564,526 |
| Southeastern CT Planning Region | 8 | 2.23% | 284,582 | 278,379 |
| Northwest Hills Planning Region | 9 | 2.2% | 114,664 | 112,199 |
Connecticut's counties show varied growth patterns from 2020 to 2025. Greater Bridgeport Planning Region leads with 4.82% annualized growth, followed by Western CT Planning Region (4.05%) and Naugatuck Valley Planning Region (3.96%). The largest counties are Capitol Planning Region (999,690), Western CT Planning Region (643,825), and South Central CT Planning Region (580,517). All 9 counties in Connecticut are growing. Overall, counties averaged 3.36% annualized growth, with total population growing by 3.55% annually.
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