| 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 |
| Jefferson County | 45 932 | 46 083 | - 151 | - 0.3 |
| Barnett township | 272 | 269 | 3 | 1.1 |
| Beaver township | 544 | 551 | - 7 | - 1.3 |
| Bell township | 2 029 | 2 055 | - 26 | - 1.3 |
| Big Run borough | 686 | 699 | - 13 | - 1.9 |
| Brockway borough | 2 182 | 2 207 | - 25 | - 1.1 |
| Brookville borough | 4 230 | 4 184 | 46 | 1.1 |
| Clover township | 474 | 523 | - 49 | - 9.4 |
| Corsica borough | 354 | 337 | 17 | 5.0 |
| Eldred township | 1 277 | 1 197 | 80 | 6.7 |
| Falls Creek borough | 939 | 1 033 | - 94 | - 9.1 |
| Gaskill township | 671 | 675 | - 4 | - 0.6 |
| Heath township | 160 | 109 | 51 | 46.8 |
| Henderson township | 1 727 | 1 376 | 351 | 25.5 |
| Knox township | 1 056 | 1 014 | 42 | 4.1 |
| McCalmont township | 1 068 | 1 006 | 62 | 6.2 |
| Oliver township | 1 129 | 1 119 | 10 | 0.9 |
| Perry township | 1 289 | 1 293 | - 4 | - 0.3 |
| Pine Creek township | 1 369 | 1 413 | - 44 | - 3.1 |
| Polk township | 294 | 305 | - 11 | - 3.6 |
| Porter township | 282 | 310 | - 28 | - 9.0 |
| Punxsutawney borough | 6 271 | 6 782 | - 511 | - 7.5 |
| Reynoldsville borough | 2 710 | 2 818 | - 108 | - 3.8 |
| Ringgold township | 764 | 705 | 59 | 8.4 |
| Rose township | 1 232 | 1 198 | 34 | 2.8 |
| Snyder township | 2 432 | 2 535 | - 103 | - 4.1 |
| Summerville borough | 525 | 675 | - 150 | - 22.2 |
| Sykesville borough | 1 246 | 1 387 | - 141 | - 10.2 |
| Timblin borough | 151 | 165 | - 14 | - 8.5 |
| Union township | 816 | 733 | 83 | 11.3 |
| Warsaw township | 1 346 | 1 213 | 133 | 11.0 |
| Washington township | 1 931 | 1 939 | - 8 | - 0.4 |
| Winslow township | 2 591 | 2 526 | 65 | 2.6 |
| Worthville borough | 85 | 65 | 20 | 30.8 |
| Young township | 1 800 | 1 667 | 133 | 8.0 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||