11 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Le Mars | 1 | 10,708 | 10,605 | 0.16% | 1,219 | 9 | City |
| Remsen | 2 | 1,686 | 1,671 | 0.18% | 1,152 | 1 | City |
| Akron | 3 | 1,543 | 1,549 | -0.06% | 1,252 | 1 | City |
| Kingsley | 4 | 1,390 | 1,402 | -0.14% | 861 | 2 | City |
| Hinton | 5 | 972 | 932 | 0.73% | 1,086 | 1 | City |
| Merrill | 6 | 710 | 719 | -0.14% | 1,368 | 1 | City |
| Brunsville | 7 | 128 | 127 | 0% | 549 | 0 | City |
| Westfield | 8 | 120 | 122 | 0% | 909 | 0 | City |
| Oyens | 9 | 87 | 89 | 0% | 770 | 0 | City |
| Craig | 10 | 78 | 77 | 0% | 886 | 0 | City |
| Struble | 11 | 71 | 73 | 0% | 455 | 0 | City |
Le Mars is the largest city in Plymouth County, with a population of 10,708.
Struble is the smallest city in Plymouth County, with a population of 71.
There are 11 cities in Plymouth County, Iowa.