26 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wilmington | 1 | 73,759 | 70,842 | 0.8% | 6,770 | 11 | City |
| Newark | 2 | 30,483 | 30,598 | -0.08% | 3,218 | 9 | City |
| Middletown | 3 | 26,259 | 23,392 | 2.23% | 2,071 | 13 | Town |
| Bear | 4 | 23,995 | 21,397 | 1.3% | 4,149 | 6 | CDP |
| Glasgow | 5 | 15,681 | 15,399 | 0.59% | 1,580 | 10 | CDP |
| Brookside | 6 | 14,325 | 13,741 | -0.01% | 3,690 | 4 | CDP |
| Hockessin | 7 | 13,966 | 14,172 | 0.22% | 1,391 | 10 | CDP |
| Pike Creek Valley | 8 | 11,511 | 11,346 | 0.17% | 4,009 | 3 | CDP |
| Claymont | 9 | 10,676 | 9,343 | 1.54% | 4,963 | 2 | CDP |
| North Star | 10 | 8,468 | 7,546 | 0.39% | 1,245 | 7 | CDP |
| Wilmington Manor | 11 | 8,353 | 8,335 | 0.37% | 5,112 | 2 | CDP |
| Pike Creek | 12 | 6,744 | 6,987 | -1.13% | 2,508 | 3 | CDP |
| Edgemoor | 13 | 6,687 | 6,483 | 1.01% | 3,486 | 2 | CDP |
| Elsmere | 14 | 6,236 | 6,223 | 0.03% | 6,318 | 1 | Town |
| New Castle | 15 | 5,758 | 5,543 | 0.75% | 1,656 | 3 | City |
| Townsend | 16 | 2,990 | 2,743 | 1.67% | 2,821 | 1 | Town |
| Greenville | 17 | 2,948 | 2,448 | 1.41% | 1,054 | 3 | CDP |
| Delaware City | 18 | 1,945 | 1,883 | 0.62% | 1,045 | 2 | City |
| St. Georges | 19 | 1,630 | 1,045 | 7.17% | 1,182 | 1 | CDP |
| Bellefonte | 20 | 1,255 | 1,225 | 0.48% | 7,090 | 0 | Town |
| Newport | 21 | 909 | 908 | 0% | 1,946 | 0 | Town |
| Arden | 22 | 438 | 430 | 0.23% | 1,759 | 0 | Village |
| Odessa | 23 | 366 | 365 | 0% | 722 | 1 | Town |
| Ardentown | 24 | 259 | 254 | 0.39% | 1,107 | 0 | Village |
| Ardencroft | 25 | 235 | 228 | 0.43% | 2,640 | 0 | Village |
| Port Penn | 26 | 172 | 293 | 6.83% | 426 | 0 | CDP |
Wilmington is the largest city in New Castle County, with a population of 73,759.
Port Penn is the smallest city in New Castle County, with a population of 172.
There are 26 cities in New Castle County, Delaware.