| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Sioux Center | 1 | 9,004 | 8,240 | 1.58% | 1,344 | 7 | City |
| Orange City | 2 | 6,537 | 6,275 | 1.07% | 1,418 | 5 | City |
| Rock Valley | 3 | 4,182 | 4,069 | -0.14% | 937 | 4 | City |
| Hawarden | 4 | 2,651 | 2,699 | -0.53% | 957 | 3 | City |
| Hull | 5 | 2,484 | 2,366 | 1.1% | 1,755 | 1 | City |
| Alton | 6 | 1,257 | 1,238 | 0.24% | 661 | 2 | City |
| Hospers | 7 | 687 | 720 | -0.58% | 1,301 | 1 | City |
| Boyden | 8 | 686 | 703 | -0.29% | 1,003 | 1 | City |
| Ireton | 9 | 564 | 581 | -0.53% | 553 | 1 | City |
| Granville | 10 | 296 | 311 | -1% | 1,017 | 0 | City |
| Maurice | 11 | 268 | 267 | 0.37% | 445 | 1 | City |
| Matlock | 12 | 76 | 77 | 0% | 201 | 0 | City |
| Chatsworth | 13 | 74 | 73 | 0% | 149 | 0 | City |
Sioux Center is the largest city in Sioux County, with a population of 9,004.
Chatsworth is the smallest city in Sioux County, with a population of 74.
There are 13 cities in Sioux County, Iowa.