| 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 |
| Beaver County | 181 412 | 186 093 | - 4 681 | - 2.5 |
| Aliquippa city | 11 734 | 13 374 | - 1 640 | - 12.3 |
| Ambridge borough | 7 769 | 8 133 | - 364 | - 4.5 |
| Baden borough | 4 377 | 5 074 | - 697 | - 13.7 |
| Beaver borough | 4 775 | 5 028 | - 253 | - 5.0 |
| Beaver Falls city | 9 920 | 10 687 | - 767 | - 7.2 |
| Big Beaver borough | 2 186 | 2 298 | - 112 | - 4.9 |
| Bridgewater borough | 739 | 751 | - 12 | - 1.6 |
| Brighton township | 8 024 | 7 489 | 535 | 7.1 |
| Center township | 11 492 | 10 742 | 750 | 7.0 |
| Chippewa township | 7 021 | 6 988 | 33 | 0.5 |
| Conway borough | 2 290 | 2 424 | - 134 | - 5.5 |
| Darlington borough | 299 | 311 | - 12 | - 3.9 |
| Darlington township | 1 974 | 2 040 | - 66 | - 3.2 |
| Daugherty township | 3 441 | 3 433 | 8 | 0.2 |
| East Rochester borough | 623 | 672 | - 49 | - 7.3 |
| Eastvale borough | 293 | 328 | - 35 | - 10.7 |
| Economy borough | 9 363 | 9 519 | - 156 | - 1.6 |
| Ellwood City borough | 732 | 850 | - 118 | - 13.9 |
| Fallston borough | 307 | 392 | - 85 | - 21.7 |
| Frankfort Springs borough | 130 | 134 | - 4 | - 3.0 |
| Franklin township | 4 307 | 3 821 | 486 | 12.7 |
| Freedom borough | 1 763 | 1 897 | - 134 | - 7.1 |
| Georgetown borough | 182 | 194 | - 12 | - 6.2 |
| Glasgow borough | 63 | 74 | - 11 | - 14.9 |
| Greene township | 2 705 | 2 573 | 132 | 5.1 |
| Hanover township | 3 529 | 3 470 | 59 | 1.7 |
| Harmony township | 3 373 | 3 694 | - 321 | - 8.7 |
| Homewood borough | 147 | 162 | - 15 | - 9.3 |
| Hookstown borough | 152 | 169 | - 17 | - 10.1 |
| Hopewell township | 13 254 | 13 274 | - 20 | - 0.2 |
| Independence township | 2 802 | 2 563 | 239 | 9.3 |
| Industry borough | 1 921 | 2 124 | - 203 | - 9.6 |
| Koppel borough | 856 | 1 024 | - 168 | - 16.4 |
| Marion township | 940 | 909 | 31 | 3.4 |
| Midland borough | 3 137 | 3 321 | - 184 | - 5.5 |
| Monaca borough | 6 286 | 6 739 | - 453 | - 6.7 |
| New Brighton borough | 6 641 | 6 854 | - 213 | - 3.1 |
| New Galilee borough | 424 | 500 | - 76 | - 15.2 |
| New Sewickley township | 7 076 | 6 861 | 215 | 3.1 |
| North Sewickley township | 6 120 | 6 178 | - 58 | - 0.9 |
| Ohioville borough | 3 759 | 3 865 | - 106 | - 2.7 |
| Patterson township | 3 197 | 3 074 | 123 | 4.0 |
| Patterson Heights borough | 670 | 576 | 94 | 16.3 |
| Potter township | 580 | 546 | 34 | 6.2 |
| Pulaski township | 1 674 | 1 697 | - 23 | - 1.4 |
| Raccoon township | 3 397 | 3 426 | - 29 | - 0.8 |
| Rochester borough | 4 014 | 4 156 | - 142 | - 3.4 |
| Rochester township | 3 129 | 3 247 | - 118 | - 3.6 |
| Shippingport borough | 237 | 227 | 10 | 4.4 |
| South Beaver township | 2 974 | 2 942 | 32 | 1.1 |
| South Heights borough | 542 | 647 | - 105 | - 16.2 |
| Vanport township | 1 451 | 1 700 | - 249 | - 14.6 |
| West Mayfield borough | 1 187 | 1 312 | - 125 | - 9.5 |
| White township | 1 434 | 1 610 | - 176 | - 10.9 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||