45 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Butler | 1 | 17,051 | 17,227 | 0.29% | 789 | 22 | Township |
| Adams | 2 | 15,867 | 14,855 | 0.51% | 710 | 22 | Township |
| Butler | 3 | 12,772 | 13,486 | -0.92% | 4,697 | 3 | City |
| Butler | 4 | 10,447 | 9,508 | 1.49% | 310 | 34 | Township |
| Slippery Rock | 5 | 8,330 | 6,711 | -0.39% | 323 | 26 | Township |
| Buffalo | 6 | 8,215 | 7,933 | 0.18% | 340 | 24 | Township |
| Center | 7 | 7,680 | 7,894 | -0.61% | 315 | 24 | Township |
| Middlesex | 8 | 7,524 | 6,889 | 0.57% | 325 | 23 | Township |
| Butler | 9 | 5,122 | 4,906 | 0.73% | 197 | 26 | Township |
| Summit | 10 | 4,282 | 4,495 | -0.83% | 191 | 22 | Township |
| Connoquenessing | 11 | 4,137 | 4,254 | -0.24% | 182 | 23 | Township |
| Slippery Rock | 12 | 3,754 | 3,166 | 2.68% | 2,282 | 2 | Borough |
| Zelienople | 13 | 3,701 | 3,905 | -0.91% | 1,803 | 2 | Borough |
| Forward | 14 | 3,448 | 3,206 | 1% | 150 | 23 | Township |
| Harmony | 15 | 3,090 | 3,190 | -0.32% | 1,062 | 3 | Township |
| Slippery Rock | 16 | 2,834 | 2,911 | -0.46% | 96 | 30 | Township |
| Oakland | 17 | 2,670 | 2,773 | -0.63% | 113 | 24 | Township |
| Butler | 18 | 2,668 | 2,550 | 0.83% | 111 | 24 | Township |
| Clay | 19 | 2,440 | 2,546 | -0.69% | 97 | 25 | Township |
| Muddy Creek | 20 | 2,143 | 2,207 | -0.46% | 95 | 23 | Township |
| Evans City | 21 | 1,656 | 1,746 | -0.9% | 2,024 | 1 | Borough |
| Mars | 22 | 1,392 | 1,460 | -0.78% | 2,962 | 0 | Borough |
| Saxonburg | 23 | 1,353 | 1,428 | -0.88% | 1,493 | 1 | Borough |
| Worth | 24 | 1,346 | 1,399 | -0.52% | 54 | 25 | Township |
| Brady | 25 | 1,164 | 1,215 | -0.94% | 69 | 17 | Township |
| Prospect | 26 | 1,063 | 1,120 | -0.84% | 260 | 4 | Borough |
| Cherry | 27 | 1,037 | 1,051 | -0.19% | 40 | 26 | Township |
| Harmony | 28 | 902 | 950 | -0.88% | 2,289 | 0 | Borough |
| Chicora | 29 | 870 | 917 | -0.91% | 1,632 | 1 | Borough |
| Connoquenessing | 30 | 842 | 674 | 3.44% | 621 | 1 | Borough |
| Harrisville | 31 | 778 | 819 | -0.89% | 968 | 1 | Borough |
| Valencia | 32 | 756 | 539 | 5% | 2,224 | 0 | Borough |
| East Butler | 33 | 722 | 763 | -0.96% | 692 | 1 | Borough |
| Allegheny | 34 | 608 | 621 | 0.16% | 24 | 25 | Township |
| Harmony | 35 | 514 | 512 | 0.59% | 16 | 31 | Township |
| Harmony | 36 | 422 | 463 | -2.31% | 12 | 34 | Township |
| Bruin | 37 | 393 | 419 | -1.01% | 215 | 2 | Borough |
| Callery | 38 | 339 | 359 | -0.88% | 631 | 1 | Borough |
| West Liberty | 39 | 317 | 335 | -0.94% | 83 | 4 | Borough |
| Eau Claire | 40 | 289 | 306 | -1.03% | 227 | 1 | Borough |
| Portersville | 41 | 221 | 233 | -0.9% | 278 | 1 | Borough |
| Barkeyville | 42 | 182 | 188 | -0.55% | 55 | 3 | Borough |
| West Sunbury | 43 | 173 | 182 | -0.57% | 1,573 | 0 | Borough |
| Petrolia | 44 | 170 | 179 | -0.58% | 430 | 0 | Borough |
| Karns City | 45 | 163 | 172 | -0.61% | 449 | 0 | Borough |
Butler is the largest city in Butler County, with a population of 17,051.
Karns City is the smallest city in Butler County, with a population of 163.
There are 45 cities in Butler County, Pennsylvania.