45 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Butler | 1 | 17,002 | 17,227 | 0.29% | 786 | 22 | Township |
| Adams | 2 | 15,786 | 14,855 | 0.52% | 707 | 22 | Township |
| Butler | 3 | 12,891 | 13,486 | -0.91% | 4,741 | 3 | City |
| Butler | 4 | 10,294 | 9,508 | 1.51% | 306 | 34 | Township |
| Slippery Rock | 5 | 8,363 | 6,711 | -0.39% | 324 | 26 | Township |
| Buffalo | 6 | 8,200 | 7,933 | 0.18% | 340 | 24 | Township |
| Center | 7 | 7,727 | 7,894 | -0.6% | 317 | 24 | Township |
| Middlesex | 8 | 7,481 | 6,889 | 0.58% | 324 | 23 | Township |
| Butler | 9 | 5,085 | 4,906 | 0.73% | 195 | 26 | Township |
| Summit | 10 | 4,318 | 4,495 | -0.83% | 192 | 22 | Township |
| Connoquenessing | 11 | 4,147 | 4,254 | -0.24% | 182 | 23 | Township |
| Zelienople | 12 | 3,735 | 3,905 | -0.9% | 1,819 | 2 | Borough |
| Slippery Rock | 13 | 3,656 | 3,166 | 2.75% | 2,222 | 2 | Borough |
| Forward | 14 | 3,414 | 3,206 | 1.01% | 148 | 23 | Township |
| Harmony | 15 | 3,100 | 3,190 | -0.32% | 1,066 | 3 | Township |
| Slippery Rock | 16 | 2,847 | 2,911 | -0.45% | 96 | 30 | Township |
| Oakland | 17 | 2,687 | 2,773 | -0.63% | 113 | 24 | Township |
| Butler | 18 | 2,646 | 2,550 | 0.84% | 110 | 24 | Township |
| Clay | 19 | 2,457 | 2,546 | -0.69% | 98 | 25 | Township |
| Muddy Creek | 20 | 2,153 | 2,207 | -0.46% | 95 | 23 | Township |
| Evans City | 21 | 1,671 | 1,746 | -0.89% | 2,043 | 1 | Borough |
| Mars | 22 | 1,403 | 1,460 | -0.85% | 2,985 | 0 | Borough |
| Saxonburg | 23 | 1,365 | 1,428 | -0.94% | 1,507 | 1 | Borough |
| Worth | 24 | 1,353 | 1,399 | -0.51% | 54 | 25 | Township |
| Brady | 25 | 1,175 | 1,215 | -0.93% | 69 | 17 | Township |
| Prospect | 26 | 1,072 | 1,120 | -0.92% | 263 | 4 | Borough |
| Cherry | 27 | 1,039 | 1,051 | -0.19% | 41 | 26 | Township |
| Harmony | 28 | 910 | 950 | -0.87% | 2,310 | 0 | Borough |
| Chicora | 29 | 878 | 917 | -0.9% | 1,647 | 1 | Borough |
| Connoquenessing | 30 | 814 | 674 | 3.56% | 601 | 1 | Borough |
| Harrisville | 31 | 785 | 819 | -0.88% | 976 | 1 | Borough |
| East Butler | 32 | 729 | 763 | -0.95% | 699 | 1 | Borough |
| Valencia | 33 | 720 | 539 | 5.26% | 2,118 | 0 | Borough |
| Allegheny | 34 | 607 | 621 | 0.17% | 24 | 25 | Township |
| Harmony | 35 | 511 | 512 | 0.59% | 16 | 31 | Township |
| Harmony | 36 | 432 | 463 | -2.26% | 13 | 34 | Township |
| Bruin | 37 | 397 | 419 | -1.24% | 218 | 2 | Borough |
| Callery | 38 | 342 | 359 | -1.16% | 637 | 1 | Borough |
| West Liberty | 39 | 320 | 335 | -0.93% | 83 | 4 | Borough |
| Eau Claire | 40 | 292 | 306 | -1.02% | 229 | 1 | Borough |
| Portersville | 41 | 223 | 233 | -0.89% | 281 | 1 | Borough |
| Barkeyville | 42 | 183 | 188 | -0.54% | 55 | 3 | Borough |
| West Sunbury | 43 | 174 | 182 | -1.14% | 1,582 | 0 | Borough |
| Petrolia | 44 | 171 | 179 | -1.16% | 433 | 0 | Borough |
| Karns City | 45 | 164 | 172 | -1.2% | 452 | 0 | Borough |
Butler is the largest city in Butler County, with a population of 17,002.
Karns City is the smallest city in Butler County, with a population of 164.
There are 45 cities in Butler County, Pennsylvania.