13 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Newton | 1 | 15,688 | 15,750 | -0.06% | 1,394 | 11 | City |
| Colfax | 2 | 2,330 | 2,254 | 0.56% | 910 | 3 | City |
| Monroe | 3 | 2,047 | 1,968 | 0.64% | 1,206 | 2 | City |
| Prairie City | 4 | 1,734 | 1,698 | 0.35% | 1,396 | 1 | City |
| Baxter | 5 | 989 | 971 | 0.3% | 1,512 | 1 | City |
| Sully | 6 | 896 | 880 | 0.34% | 1,540 | 1 | City |
| Kellogg | 7 | 595 | 601 | -0.17% | 1,604 | 0 | City |
| Lynnville | 8 | 382 | 382 | 0% | 348 | 1 | City |
| Mingo | 9 | 319 | 303 | 0.95% | 518 | 1 | City |
| Oakland Acres | 10 | 179 | 175 | 0.56% | 628 | 0 | City |
| Lambs Grove | 11 | 174 | 174 | 0% | 1,706 | 0 | City |
| Reasnor | 12 | 158 | 155 | 0.64% | 285 | 1 | City |
| Valeria | 13 | 42 | 39 | 2.44% | 857 | 0 | City |
Newton is the largest city in Jasper County, with a population of 15,688.
Valeria is the smallest city in Jasper County, with a population of 42.
There are 13 cities in Jasper County, Iowa.