| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wilmington | 1 | 74,084 | 70,889 | 0.78% | 6,800 | 11 | City |
| Newark | 2 | 30,311 | 30,611 | -0.16% | 3,199 | 9 | City |
| Middletown | 3 | 26,341 | 23,379 | 2.1% | 1,950 | 14 | Town |
| Elsmere | 4 | 6,196 | 6,219 | 0% | 6,278 | 1 | Town |
| New Castle | 5 | 5,766 | 5,538 | 0.7% | 1,658 | 3 | City |
| Townsend | 6 | 3,031 | 2,751 | 1.54% | 2,859 | 1 | Town |
| Delaware City | 7 | 1,951 | 1,882 | 0.62% | 1,048 | 2 | City |
| Bellefonte | 8 | 1,319 | 1,285 | 0.46% | 7,452 | 0 | Town |
| Newport | 9 | 906 | 909 | 0% | 1,940 | 0 | Town |
| Arden | 10 | 444 | 432 | 0.45% | 1,783 | 0 | Village |
| Odessa | 11 | 359 | 362 | -0.28% | 708 | 1 | Town |
| Ardentown | 12 | 258 | 252 | 0.39% | 1,103 | 0 | Village |
| Ardencroft | 13 | 233 | 228 | 0.43% | 2,618 | 0 | Village |
Wilmington is the largest city in New Castle County, with a population of 74,084.
Ardencroft is the smallest city in New Castle County, with a population of 233.
There are 13 cities in New Castle County, Delaware.