| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Missouri Valley | 1 | 2,603 | 2,674 | -0.5% | 784 | 3 | City |
| Woodbine | 2 | 1,723 | 1,623 | 1.06% | 1,040 | 2 | City |
| Logan | 3 | 1,343 | 1,386 | -0.67% | 1,355 | 1 | City |
| Dunlap | 4 | 1,026 | 1,046 | -0.39% | 822 | 1 | City |
| Mondamin | 5 | 331 | 334 | -0.3% | 732 | 0 | City |
| Persia | 6 | 288 | 294 | -0.35% | 575 | 1 | City |
| Modale | 7 | 284 | 274 | 0.71% | 273 | 1 | City |
| Pisgah | 8 | 248 | 246 | 0% | 496 | 1 | City |
| Magnolia | 9 | 196 | 194 | 0% | 321 | 1 | City |
| Little Sioux | 10 | 178 | 169 | 0.56% | 475 | 0 | City |
Missouri Valley is the largest city in Harrison County, with a population of 2,603.
Little Sioux is the smallest city in Harrison County, with a population of 178.
There are 10 cities in Harrison County, Iowa.