| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Newton | 1 | 15,732 | 15,748 | -0.06% | 1,398 | 11 | City |
| Colfax | 2 | 2,315 | 2,255 | 0.52% | 904 | 3 | City |
| Monroe | 3 | 2,035 | 1,970 | 0.64% | 1,198 | 2 | City |
| Prairie City | 4 | 1,730 | 1,698 | 0.35% | 1,393 | 1 | City |
| Baxter | 5 | 987 | 970 | 0.3% | 1,509 | 1 | City |
| Sully | 6 | 893 | 882 | 0.22% | 1,534 | 1 | City |
| Kellogg | 7 | 598 | 601 | -0.17% | 1,612 | 0 | City |
| Lynnville | 8 | 383 | 382 | 0% | 348 | 1 | City |
| Mingo | 9 | 315 | 304 | 0.64% | 511 | 1 | City |
| Oakland Acres | 10 | 178 | 175 | 0% | 625 | 0 | City |
| Lambs Grove | 11 | 171 | 173 | 0% | 1,676 | 0 | City |
| Reasnor | 12 | 158 | 156 | 0% | 285 | 1 | City |
| Valeria | 13 | 41 | 39 | 0% | 837 | 0 | City |
Newton is the largest city in Jasper County, with a population of 15,732.
Valeria is the smallest city in Jasper County, with a population of 41.
There are 13 cities in Jasper County, Iowa.