| 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 |
| Somerset County | 80 023 | 78 218 | 1 805 | 2.3 |
| Addison borough | 214 | 212 | 2 | 0.9 |
| Addison township | 1 019 | 946 | 73 | 7.7 |
| Allegheny township | 654 | 695 | - 41 | - 5.9 |
| Benson borough | 194 | 277 | - 83 | - 30.0 |
| Berlin borough | 2 192 | 2 064 | 128 | 6.2 |
| Black township | 980 | 942 | 38 | 4.0 |
| Boswell borough | 1 364 | 1 485 | - 121 | - 8.1 |
| Brothersvalley township | 4 184 | 2 395 | 1 789 | 74.7 |
| Callimont borough | 51 | 55 | - 4 | - 7.3 |
| Casselman borough | 99 | 89 | 10 | 11.2 |
| Central City borough | 1 258 | 1 246 | 12 | 1.0 |
| Conemaugh township | 7 452 | 7 737 | - 285 | - 3.7 |
| Confluence borough | 834 | 873 | - 39 | - 4.5 |
| Elk Lick township | 2 293 | 2 313 | - 20 | - 0.9 |
| Fairhope township | 137 | 137 | 0 | 0.0 |
| Garrett borough | 449 | 520 | - 71 | - 13.7 |
| Greenville township | 718 | 664 | 54 | 8.1 |
| Hooversville borough | 779 | 731 | 48 | 6.6 |
| Indian Lake borough | 450 | 388 | 62 | 16.0 |
| Jefferson township | 1 375 | 1 462 | - 87 | - 6.0 |
| Jenner township | 4 054 | 4 147 | - 93 | - 2.2 |
| Jennerstown borough | 714 | 635 | 79 | 12.4 |
| Larimer township | 590 | 547 | 43 | 7.9 |
| Lincoln township | 1 669 | 1 655 | 14 | 0.8 |
| Lower Turkeyfoot township | 672 | 670 | 2 | 0.3 |
| Meyersdale borough | 2 473 | 2 518 | - 45 | - 1.8 |
| Middlecreek township | 797 | 764 | 33 | 4.3 |
| Milford township | 1 561 | 1 544 | 17 | 1.1 |
| New Baltimore borough | 168 | 162 | 6 | 3.7 |
| New Centerville borough | 193 | 211 | - 18 | - 8.5 |
| Northampton township | 366 | 356 | 10 | 2.8 |
| Ogle township | 588 | 597 | - 9 | - 1.5 |
| Paint borough | 1 103 | 1 091 | 12 | 1.1 |
| Paint township | 3 300 | 3 491 | - 191 | - 5.5 |
| Quemahoning township | 2 180 | 2 301 | - 121 | - 5.3 |
| Rockwood borough | 954 | 1 014 | - 60 | - 5.9 |
| Salisbury borough | 878 | 716 | 162 | 22.6 |
| Seven Springs borough | 126 | 22 | 104 | 472.7 |
| Shade township | 2 886 | 3 177 | - 291 | - 9.2 |
| Shanksville borough | 245 | 235 | 10 | 4.3 |
| Somerset borough | 6 762 | 6 454 | 308 | 4.8 |
| Somerset township | 9 319 | 8 732 | 587 | 6.7 |
| Southampton township | 655 | 553 | 102 | 18.4 |
| Stonycreek township | 2 221 | 2 083 | 138 | 6.6 |
| Stoystown borough | 428 | 389 | 39 | 10.0 |
| Summit township | 2 368 | 2 495 | - 127 | - 5.1 |
| Upper Turkeyfoot township | 1 232 | 1 132 | 100 | 8.8 |
| Ursina borough | 254 | 327 | - 73 | - 22.3 |
| Wellersburg borough | 176 | 213 | - 37 | - 17.4 |
| Windber borough | 4 395 | 4 756 | - 361 | - 7.6 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||