| 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 |
| Indiana County | 89 605 | 89 994 | - 389 | - 0.4 |
| Armagh borough | 131 | 104 | 27 | 26.0 |
| Armstrong township | 3 090 | 3 048 | 42 | 1.4 |
| Banks township | 997 | 995 | 2 | 0.2 |
| Black Lick township | 1 317 | 1 314 | 3 | 0.2 |
| Blairsville borough | 3 607 | 3 595 | 12 | 0.3 |
| Brush Valley township | 1 881 | 1 811 | 70 | 3.9 |
| Buffington township | 1 275 | 1 217 | 58 | 4.8 |
| Burrell township | 3 746 | 3 669 | 77 | 2.1 |
| Canoe township | 1 670 | 1 915 | - 245 | - 12.8 |
| Center township | 4 876 | 5 257 | - 381 | - 7.2 |
| Cherryhill township | 2 842 | 2 764 | 78 | 2.8 |
| Cherry Tree borough | 443 | 431 | 12 | 2.8 |
| Clymer borough | 1 547 | 1 499 | 48 | 3.2 |
| Conemaugh township | 2 437 | 2 448 | - 11 | - 0.4 |
| Creekside borough | 323 | 337 | - 14 | - 4.2 |
| East Mahoning township | 1 196 | 1 140 | 56 | 4.9 |
| East Wheatfield township | 2 607 | 2 735 | - 128 | - 4.7 |
| Ernest borough | 501 | 492 | 9 | 1.8 |
| Glen Campbell borough | 306 | 313 | - 7 | - 2.2 |
| Grant township | 696 | 729 | - 33 | - 4.5 |
| Green township | 3 995 | 4 095 | - 100 | - 2.4 |
| Homer City borough | 1 844 | 1 809 | 35 | 1.9 |
| Indiana borough | 14 895 | 15 174 | - 279 | - 1.8 |
| Marion Center borough | 451 | 476 | - 25 | - 5.3 |
| Montgomery township | 1 706 | 1 729 | - 23 | - 1.3 |
| North Mahoning township | 1 383 | 1 254 | 129 | 10.3 |
| Pine township | 2 140 | 2 172 | - 32 | - 1.5 |
| Plumville borough | 342 | 390 | - 48 | - 12.3 |
| Rayne township | 3 292 | 3 339 | - 47 | - 1.4 |
| Saltsburg borough | 955 | 990 | - 35 | - 3.5 |
| Shelocta borough | 127 | 108 | 19 | 17.6 |
| Smicksburg borough | 49 | 76 | - 27 | - 35.5 |
| South Mahoning township | 1 852 | 1 713 | 139 | 8.1 |
| Washington township | 1 805 | 1 861 | - 56 | - 3.0 |
| West Mahoning township | 1 128 | 1 032 | 96 | 9.3 |
| West Wheatfield township | 2 375 | 2 370 | 5 | 0.2 |
| White township | 14 034 | 13 788 | 246 | 1.8 |
| Young township | 1 744 | 1 805 | - 61 | - 3.4 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||