| Population Change 1990-2000 | ||||
| County or Municipality | 2000 Population | 1990 Population | Population Change | Percent Change |
| Pennsylvania | 12 281 054 | 11 881 643 | 399 411 | 3.4 |
| Lawrence County | 94 643 | 96 246 | - 1 603 | - 1.7 |
| Bessemer borough | 1 172 | 1 196 | - 24 | - 2.0 |
| Ellport borough | 1 148 | 1 243 | - 95 | - 7.6 |
| Ellwood City borough | 7 956 | 8 044 | - 88 | - 1.1 |
| Enon Valley borough | 387 | 355 | 32 | 9.0 |
| Hickory township | 2 356 | 2 317 | 39 | 1.7 |
| Little Beaver township | 1 310 | 1 251 | 59 | 4.7 |
| Mahoning township | 3 447 | 3 560 | - 113 | - 3.2 |
| Neshannock township | 9 216 | 8 373 | 843 | 10.1 |
| New Beaver borough | 1 677 | 1 736 | - 59 | - 3.4 |
| New Castle city | 26 309 | 28 334 | - 2 025 | - 7.1 |
| New Wilmington borough | 2 452 | 2 706 | - 254 | - 9.4 |
| North Beaver township | 4 022 | 3 982 | 40 | 1.0 |
| Perry township | 1 930 | 1 841 | 89 | 4.8 |
| Plain Grove township | 854 | 791 | 63 | 8.0 |
| Pulaski township | 3 658 | 3 469 | 189 | 5.4 |
| Scott township | 2 235 | 2 200 | 35 | 1.6 |
| Shenango township | 7 633 | 7 187 | 446 | 6.2 |
| Slippery Rock township | 3 179 | 3 196 | - 17 | - 0.5 |
| S.N.P.J. borough | 0 | 12 | - 12 | - 100.0 |
| South New Castle borough | 808 | 805 | 3 | 0.4 |
| Taylor township | 1 198 | 1 326 | - 128 | - 9.7 |
| Union township | 5 103 | 5 581 | - 478 | - 8.6 |
| Volant borough | 113 | 152 | - 39 | - 25.7 |
| Wampum borough | 678 | 666 | 12 | 1.8 |
| Washington township | 714 | 671 | 43 | 6.4 |
| Wayne township | 2 328 | 2 785 | - 457 | - 16.4 |
| Wilmington township | 2 760 | 2 467 | 293 | 11.9 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||