25 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Milford | 1 | 14,771 | 11,310 | 4.92% | 1,499 | 10 | City |
| Seaford | 2 | 9,194 | 7,982 | 2.7% | 1,801 | 5 | City |
| Georgetown | 3 | 8,324 | 7,193 | 2.79% | 1,658 | 5 | Town |
| Millsboro | 4 | 8,094 | 6,943 | 2.92% | 1,584 | 5 | Town |
| Laurel | 5 | 4,519 | 3,896 | 2.82% | 1,631 | 3 | Town |
| Milton | 6 | 3,882 | 3,335 | 2.89% | 1,458 | 3 | Town |
| Lewes | 7 | 3,797 | 3,320 | 2.57% | 906 | 4 | City |
| Selbyville | 8 | 3,379 | 2,907 | 2.86% | 833 | 4 | Town |
| Ocean View | 9 | 3,113 | 2,663 | 2.98% | 1,101 | 3 | Town |
| Bridgeville | 10 | 2,992 | 2,574 | 2.85% | 621 | 5 | Town |
| Delmar | 11 | 2,337 | 2,040 | 2.59% | 1,229 | 2 | Town |
| Millville | 12 | 2,170 | 1,857 | 2.94% | 852 | 3 | Town |
| Blades | 13 | 1,367 | 1,179 | 2.78% | 2,472 | 1 | Town |
| Rehoboth Beach | 14 | 1,292 | 1,115 | 2.78% | 1,100 | 1 | City |
| Greenwood | 15 | 1,155 | 994 | 2.85% | 1,455 | 1 | Town |
| Bethany Beach | 16 | 1,114 | 957 | 2.86% | 970 | 1 | Town |
| Dagsboro | 17 | 1,016 | 874 | 2.83% | 707 | 1 | Town |
| Frankford | 18 | 930 | 805 | 2.76% | 802 | 1 | Town |
| Ellendale | 19 | 571 | 493 | 2.7% | 391 | 1 | Town |
| South Bethany | 20 | 535 | 460 | 2.88% | 1,064 | 1 | Town |
| Dewey Beach | 21 | 416 | 358 | 2.72% | 1,257 | 0 | Town |
| Fenwick Island | 22 | 400 | 344 | 2.83% | 1,208 | 0 | Town |
| Bethel | 23 | 274 | 239 | 2.62% | 623 | 0 | Town |
| Henlopen Acres | 24 | 162 | 140 | 2.53% | 635 | 0 | Town |
| Galestown | 25 | 115 | 114 | 0% | 489 | 0 | Town |
Milford is the largest city in Sussex County, with a population of 14,771.
Galestown is the smallest city in Sussex County, with a population of 115.
There are 25 cities in Sussex County, Delaware.