42 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Butler township | 1 | 16,749 | 17,230 | -0.2% | 775 | 21.62 | Township |
| Adams township | 2 | 16,155 | 14,854 | 1.74% | 723 | 22.34 | Township |
| Butler | 3 | 12,842 | 13,484 | -0.99% | 4,723 | 2.72 | City |
| Butler township | 4 | 10,130 | 9,504 | 0.95% | 301 | 33.65 | Township |
| Slippery Rock township | 5 | 8,392 | 6,712 | -0.2% | 326 | 25.78 | Township |
| Buffalo township | 6 | 8,323 | 7,925 | 1.04% | 345 | 24.15 | Township |
| Center township | 7 | 7,824 | 7,892 | 0.09% | 321 | 24.39 | Township |
| Middlesex township | 8 | 7,465 | 6,889 | 0.61% | 323 | 23.12 | Township |
| Butler township | 9 | 5,090 | 4,905 | 0.91% | 195 | 26.04 | Township |
| Summit township | 10 | 4,356 | 4,500 | -0.46% | 194 | 22.43 | Township |
| Connoquenessing township | 11 | 4,187 | 4,258 | 0.26% | 184 | 22.74 | Township |
| Slippery Rock | 12 | 3,853 | 3,168 | 3.69% | 2,342 | 1.65 | Borough |
| Zelienople | 13 | 3,715 | 3,905 | -1.01% | 1,810 | 2.05 | Borough |
| Forward township | 14 | 3,388 | 3,206 | 0.71% | 147 | 23.03 | Township |
| Harmony township | 15 | 3,097 | 3,188 | -0.35% | 1,065 | 2.91 | Township |
| Slippery Rock township | 16 | 2,867 | 2,912 | -0.21% | 97 | 29.65 | Township |
| Oakland township | 17 | 2,689 | 2,774 | -0.56% | 114 | 23.68 | Township |
| Butler township | 18 | 2,639 | 2,551 | 0.8% | 110 | 23.96 | Township |
| Clay township | 19 | 2,467 | 2,543 | -0.4% | 98 | 25.11 | Township |
| Muddy Creek township | 20 | 2,144 | 2,206 | -0.6% | 95 | 22.60 | Township |
| Evans City | 21 | 1,655 | 1,740 | -1.02% | 2,023 | 0.82 | Borough |
| Mars | 22 | 1,400 | 1,462 | -0.85% | 2,979 | 0.47 | Borough |
| Saxonburg | 23 | 1,358 | 1,428 | -1.02% | 1,499 | 0.91 | Borough |
| Worth township | 24 | 1,354 | 1,397 | -0.44% | 54 | 24.98 | Township |
| Brady township | 25 | 1,200 | 1,215 | 0.17% | 71 | 16.97 | Township |
| Prospect | 26 | 1,071 | 1,120 | -0.92% | 262 | 4.08 | Borough |
| Cherry township | 27 | 1,046 | 1,053 | 0.1% | 41 | 25.62 | Township |
| Harmony | 28 | 910 | 950 | -0.87% | 2,310 | 0.39 | Borough |
| Chicora | 29 | 876 | 918 | -0.91% | 1,644 | 0.53 | Borough |
| Connoquenessing | 30 | 809 | 673 | 3.45% | 597 | 1.35 | Borough |
| Valencia | 31 | 790 | 539 | 6.76% | 2,324 | 0.34 | Borough |
| Harrisville | 32 | 786 | 820 | -0.88% | 978 | 0.80 | Borough |
| East Butler | 33 | 729 | 764 | -0.95% | 699 | 1.04 | Borough |
| Bruin | 34 | 398 | 422 | -1.24% | 218 | 1.82 | Borough |
| Callery | 35 | 342 | 359 | -0.87% | 637 | 0.54 | Borough |
| West Liberty | 36 | 316 | 333 | -0.94% | 82 | 3.84 | Borough |
| Eau Claire | 37 | 293 | 308 | -1.01% | 230 | 1.27 | Borough |
| Portersville | 38 | 219 | 231 | -0.91% | 275 | 0.80 | Borough |
| Barkeyville | 39 | 181 | 190 | -1.09% | 54 | 3.32 | Borough |
| West Sunbury | 40 | 173 | 182 | -1.14% | 1,573 | 0.11 | Borough |
| Petrolia | 41 | 169 | 178 | -1.17% | 428 | 0.40 | Borough |
| Karns City | 42 | 163 | 172 | -1.21% | 449 | 0.36 | Borough |
Butler township is the largest city in Butler County, with a population of 16,749.
Karns City is the smallest city in Butler County.
There are 42 cities in Butler County, Pennsylvania.