| Numeric | Numeric | Percent | Percent | ||||
| Population | Population | Population | Population | ||||
| 1990 | 7/1/1998 | 7/1/1999 | Change | Change | Change | Change | |
| Census | Estimate | Estimate | 1990-99 | 1998-99 | 1990-99 | 1998-99 | |
| Pennsylvania | 11,881,643 | 12,002,329 | 11,994,016 | 112,373 | -8,313 | 0.9% | -0.1% |
| Adams | 78,274 | 86,660 | 87,697 | 9,423 | 1,037 | 12.0% | 1.2% |
| Allegheny | 1,336,449 | 1,267,963 | 1,256,806 | -79,643 | -11,157 | -6.0% | -0.9% |
| Armstrong | 73,478 | 73,313 | 73,001 | -477 | -312 | -0.6% | -0.4% |
| Beaver | 186,093 | 184,287 | 182,687 | -3,406 | -1,600 | -1.8% | -0.9% |
| Bedford | 47,919 | 49,405 | 49,699 | 1,780 | 294 | 3.7% | 0.6% |
| Berks | 336,523 | 355,761 | 358,211 | 21,688 | 2,450 | 6.4% | 0.7% |
| Blair | 130,542 | 130,547 | 129,937 | -605 | -610 | -0.5% | -0.5% |
| Bradford | 60,967 | 62,386 | 62,146 | 1,179 | -240 | 1.9% | -0.4% |
| Bucks | 541,174 | 587,863 | 594,047 | 52,873 | 6,184 | 9.8% | 1.1% |
| Butler | 152,013 | 170,799 | 172,522 | 20,509 | 1,723 | 13.5% | 1.0% |
| Cambria | 163,029 | 155,587 | 153,766 | -9,263 | -1,821 | -5.7% | -1.2% |
| Cameron | 5,913 | 5,612 | 5,571 | -342 | -41 | -5.8% | -0.7% |
| Carbon | 56,846 | 58,690 | 58,759 | 1,913 | 69 | 3.4% | 0.1% |
| Centre | 123,786 | 131,997 | 132,190 | 8,404 | 193 | 6.8% | 0.1% |
| Chester | 376,396 | 421,873 | 430,001 | 53,605 | 8,128 | 14.2% | 1.9% |
| Clarion | 41,699 | 41,723 | 41,651 | -48 | -72 | -0.1% | -0.2% |
| Clearfield | 78,097 | 80,722 | 80,732 | 2,635 | 10 | 3.4% | 0.0% |
| Clinton | 37,182 | 36,937 | 36,774 | -408 | -163 | -1.1% | -0.4% |
| Columbia | 63,202 | 63,906 | 63,674 | 472 | -232 | 0.7% | -0.4% |
| Crawford | 86,169 | 89,266 | 89,109 | 2,940 | -157 | 3.4% | -0.2% |
| Cumberland | 195,257 | 209,611 | 210,663 | 15,406 | 1,052 | 7.9% | 0.5% |
| Dauphin | 237,813 | 245,456 | 245,576 | 7,763 | 120 | 3.3% | 0.0% |
| Delaware | 547,651 | 542,592 | 541,502 | -6,149 | -1,090 | -1.1% | -0.2% |
| Elk | 34,878 | 34,614 | 34,344 | -534 | -270 | -1.5% | -0.8% |
| Erie | 275,572 | 278,114 | 276,993 | 1,421 | -1,121 | 0.5% | -0.4% |
| Fayette | 145,351 | 144,362 | 143,775 | -1,576 | -587 | -1.1% | -0.4% |
| Forest | 4,802 | 4,947 | 4,938 | 136 | -9 | 2.8% | -0.2% |
| Franklin | 121,082 | 128,255 | 128,812 | 7,730 | 557 | 6.4% | 0.4% |
| Fulton | 13,837 | 14,528 | 14,616 | 779 | 88 | 5.6% | 0.6% |
| Greene | 39,550 | 42,228 | 42,072 | 2,522 | -156 | 6.4% | -0.4% |
| Huntingdon | 44,164 | 44,755 | 44,753 | 589 | -2 | 1.3% | 0.0% |
| Indiana | 89,994 | 88,389 | 87,831 | -2,163 | -558 | -2.4% | -0.6% |
| Jefferson | 46,083 | 46,184 | 46,086 | 3 | -98 | 0.0% | -0.2% |
| Juniata | 20,625 | 22,119 | 22,204 | 1,579 | 85 | 7.7% | 0.4% |
| Lackawanna | 219,039 | 208,390 | 206,520 | -12,519 | -1,870 | -5.7% | -0.9% |
| Lancaster | 422,822 | 456,679 | 460,035 | 37,213 | 3,356 | 8.8% | 0.7% |
| Lawrence | 96,246 | 94,904 | 94,508 | -1,738 | -396 | -1.8% | -0.4% |
| Lebanon | 113,744 | 117,631 | 117,856 | 4,112 | 225 | 3.6% | 0.2% |
| Lehigh | 291,130 | 298,792 | 299,855 | 8,725 | 1,063 | 3.0% | 0.4% |
| Luzerne | 328,149 | 314,609 | 312,000 | -16,149 | -2,609 | -4.9% | -0.8% |
| Lycoming | 118,710 | 117,408 | 116,709 | -2,001 | -699 | -1.7% | -0.6% |
| McKean | 47,131 | 46,319 | 45,987 | -1,144 | -332 | -2.4% | -0.7% |
| Mercer | 121,003 | 121,760 | 121,458 | 455 | -302 | 0.4% | -0.2% |
| Mifflin | 46,197 | 46,965 | 46,793 | 596 | -172 | 1.3% | -0.4% |
| Monroe | 95,709 | 125,407 | 128,541 | 32,832 | 3,134 | 34.3% | 2.5% |
| Montgomery | 678,111 | 719,569 | 724,087 | 45,976 | 4,518 | 6.8% | 0.6% |
| Montour | 17,735 | 17,585 | 17,571 | -164 | -14 | -0.9% | -0.1% |
| Northampton | 247,105 | 258,568 | 259,736 | 12,631 | 1,168 | 5.1% | 0.5% |
| Northumberland | 96,771 | 93,950 | 93,163 | -3,608 | -787 | -3.7% | -0.8% |
| Perry | 41,172 | 44,273 | 44,280 | 3,108 | 7 | 7.5% | 0.0% |
| Philadelphia | 1,585,577 | 1,434,968 | 1,417,601 | -167,976 | -17,367 | -10.6% | -1.2% |
| Pike | 27,966 | 40,149 | 41,357 | 13,391 | 1,208 | 47.9% | 3.0% |
| Potter | 16,717 | 17,134 | 17,115 | 398 | -19 | 2.4% | -0.1% |
| Schuylkill | 152,585 | 150,066 | 148,788 | -3,797 | -1,278 | -2.5% | -0.9% |
| Snyder | 36,680 | 37,965 | 37,875 | 1,195 | -90 | 3.3% | -0.2% |
| Somerset | 78,218 | 80,192 | 80,028 | 1,810 | -164 | 2.3% | -0.2% |
| Sullivan | 6,104 | 6,074 | 6,038 | -66 | -36 | -1.1% | -0.6% |
| Susquehanna | 40,380 | 42,082 | 42,190 | 1,810 | 108 | 4.5% | 0.3% |
| Tioga | 41,126 | 41,522 | 41,657 | 531 | 135 | 1.3% | 0.3% |
| Union | 36,176 | 40,270 | 40,546 | 4,370 | 276 | 12.1% | 0.7% |
| Venango | 59,381 | 57,795 | 57,562 | -1,819 | -233 | -3.1% | -0.4% |
| Warren | 45,050 | 43,793 | 43,505 | -1,545 | -288 | -3.4% | -0.7% |
| Washington | 204,584 | 205,339 | 204,888 | 304 | -451 | 0.1% | -0.2% |
| Wayne | 39,944 | 45,431 | 46,080 | 6,136 | 649 | 15.4% | 1.4% |
| Westmoreland | 370,321 | 372,389 | 370,658 | 337 | -1,731 | 0.1% | -0.5% |
| Wyoming | 28,076 | 29,212 | 29,298 | 1,222 | 86 | 4.4% | 0.3% |
| York | 339,574 | 373,688 | 376,586 | 37,012 | 2,898 | 10.9% | 0.8% |