| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hermitage | 1 | 16,203 | 16,816 | -0.64% | 534 | 30 | City |
| Sharon | 2 | 12,549 | 13,127 | -0.78% | 3,327 | 4 | City |
| Grove City | 3 | 7,663 | 7,854 | -0.4% | 2,842 | 3 | Borough |
| Greenville | 4 | 5,386 | 5,517 | -0.37% | 2,854 | 2 | Borough |
| Pine | 5 | 4,715 | 4,820 | -0.32% | 186 | 25 | Township |
| Farrell | 6 | 4,081 | 4,251 | -0.71% | 1,803 | 2 | City |
| Sharpsville | 7 | 4,064 | 4,247 | -0.76% | 2,922 | 1 | Borough |
| Hempfield | 8 | 3,631 | 3,747 | -0.41% | 257 | 14 | Township |
| Shenango | 9 | 3,425 | 3,529 | -0.17% | 114 | 30 | Township |
| West Salem | 10 | 3,162 | 3,216 | -0.47% | 86 | 37 | Township |
| Pymatuning | 11 | 3,013 | 3,126 | -0.59% | 186 | 16 | Township |
| Findley | 12 | 2,929 | 2,846 | 3.61% | 138 | 21 | Township |
| South Pymatuning | 13 | 2,555 | 2,651 | -0.43% | 131 | 20 | Township |
| Lackawannock | 14 | 2,460 | 2,480 | -0.2% | 118 | 21 | Township |
| Delaware | 15 | 2,019 | 2,058 | -0.15% | 62 | 33 | Township |
| Mercer | 16 | 1,890 | 1,977 | -0.79% | 1,634 | 1 | Borough |
| East Lackawannock | 17 | 1,632 | 1,666 | -0.18% | 76 | 21 | Township |
| Wilmington | 18 | 1,411 | 1,409 | -0.35% | 108 | 13 | Township |
| Perry | 19 | 1,293 | 1,332 | -0.31% | 72 | 18 | Township |
| Sandy Lake | 20 | 1,184 | 1,197 | -0.25% | 49 | 24 | Township |
| Greene | 21 | 1,026 | 1,052 | -0.58% | 47 | 22 | Township |
| Mercer | 22 | 1,003 | 1,009 | 0.1% | 77 | 13 | Township |
| Stoneboro | 23 | 916 | 946 | -0.65% | 323 | 3 | Borough |
| Worth | 24 | 793 | 823 | -0.88% | 32 | 25 | Township |
| West Middlesex | 25 | 766 | 800 | -0.78% | 907 | 1 | Borough |
| Sandy Creek | 26 | 764 | 783 | -0.26% | 48 | 16 | Township |
| Sharon | 27 | 761 | 787 | -0.78% | 22 | 34 | Township |
| Greenville | 28 | 756 | 759 | 0.53% | 30 | 25 | Township |
| Salem | 29 | 740 | 762 | -0.54% | 55 | 13 | Township |
| French Creek | 30 | 706 | 709 | 0.14% | 34 | 21 | Township |
| Wolf Creek | 31 | 698 | 713 | -0.29% | 41 | 17 | Township |
| Lake | 32 | 676 | 700 | -0.88% | 41 | 16 | Township |
| Sandy Lake | 33 | 619 | 647 | -0.8% | 744 | 1 | Borough |
| Clark | 34 | 554 | 577 | -0.72% | 184 | 3 | Borough |
| Jamestown | 35 | 552 | 575 | -0.72% | 663 | 1 | Borough |
| Otter Creek | 36 | 506 | 524 | -0.59% | 43 | 12 | Township |
| New Vernon | 37 | 478 | 491 | -0.62% | 32 | 15 | Township |
| Deer Creek | 38 | 445 | 463 | -0.67% | 31 | 15 | Township |
| Fredonia | 39 | 413 | 433 | -0.96% | 1,157 | 0 | Borough |
| New Lebanon | 40 | 196 | 186 | 0.51% | 154 | 1 | Borough |
| Jackson Center | 41 | 187 | 196 | -1.06% | 164 | 1 | Borough |
| Sheakleyville | 42 | 144 | 150 | -0.69% | 735 | 0 | Borough |
Hermitage is the largest city in Mercer County, with a population of 16,203.
Sheakleyville is the smallest city in Mercer County, with a population of 144.
There are 42 cities in Mercer County, Pennsylvania.