| 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 |
| Armstrong County | 72 392 | 73 478 | - 1 086 | - 1.5 |
| Apollo borough | 1 765 | 1 895 | - 130 | - 6.9 |
| Applewold borough | 356 | 388 | - 32 | - 8.2 |
| Atwood borough | 112 | 128 | - 16 | - 12.5 |
| Bethel township | 1 290 | 1 261 | 29 | 2.3 |
| Boggs township | 979 | 981 | - 2 | - 0.2 |
| Bradys Bend township | 939 | 963 | - 24 | - 2.5 |
| Burrell township | 749 | 728 | 21 | 2.9 |
| Cadogan township | 390 | 427 | - 37 | - 8.7 |
| Cowanshannock township | 3 006 | 2 813 | 193 | 6.9 |
| Dayton borough | 543 | 572 | - 29 | - 5.1 |
| East Franklin township | 3 900 | 3 923 | - 23 | - 0.6 |
| Elderton borough | 358 | 371 | - 13 | - 3.5 |
| Ford City borough | 3 451 | 3 413 | 38 | 1.1 |
| Ford Cliff borough | 412 | 450 | - 38 | - 8.4 |
| Freeport borough | 1 962 | 1 983 | - 21 | - 1.1 |
| Gilpin township | 2 587 | 2 804 | - 217 | - 7.7 |
| Hovey township | 93 | 99 | - 6 | - 6.1 |
| Kiskiminetas township | 4 950 | 5 456 | - 506 | - 9.3 |
| Kittanning borough | 4 787 | 5 120 | - 333 | - 6.5 |
| Kittanning township | 2 359 | 2 310 | 49 | 2.1 |
| Leechburg borough | 2 386 | 2 504 | - 118 | - 4.7 |
| Madison township | 943 | 941 | 2 | 0.2 |
| Mahoning township | 1 502 | 1 504 | - 2 | - 0.1 |
| Manor township | 4 231 | 4 482 | - 251 | - 5.6 |
| Manorville borough | 401 | 418 | - 17 | - 4.1 |
| North Apollo borough | 1 426 | 1 391 | 35 | 2.5 |
| North Buffalo township | 2 942 | 2 897 | 45 | 1.6 |
| Parker city | 799 | 853 | - 54 | - 6.3 |
| Parks township | 2 754 | 2 739 | 15 | 0.5 |
| Perry township | 404 | 322 | 82 | 25.5 |
| Pine township | 499 | 534 | - 35 | - 6.6 |
| Plumcreek township | 2 304 | 2 400 | - 96 | - 4.0 |
| Rayburn township | 1 811 | 1 823 | - 12 | - 0.7 |
| Redbank township | 1 296 | 1 058 | 238 | 22.5 |
| Rural Valley borough | 922 | 957 | - 35 | - 3.7 |
| South Bend township | 1 259 | 1 304 | - 45 | - 3.5 |
| South Bethlehem borough | 444 | 479 | - 35 | - 7.3 |
| South Buffalo township | 2 785 | 2 687 | 98 | 3.6 |
| Sugarcreek township | 1 557 | 1 496 | 61 | 4.1 |
| Valley township | 681 | 709 | - 28 | - 3.9 |
| Washington township | 1 029 | 984 | 45 | 4.6 |
| Wayne township | 1 117 | 937 | 180 | 19.2 |
| West Franklin township | 1 935 | 2 008 | - 73 | - 3.6 |
| West Kittanning borough | 1 199 | 1 253 | - 54 | - 4.3 |
| Worthington borough | 778 | 713 | 65 | 9.1 |
| Source: U.S. Census Bureau | Prepared by: Pennsylvania State Data Center | |||