1880
| RANK | COUNTY | TOTAL POPULATION | RANK | COUNTY | TOTAL POPULATION | |
| 1 | Philadelphia County | 847,170 | 46 | Adams County | 32,455 | |
| 2 | Allegheny County | 355,869 | 2 | Allegheny County | 355,869 | |
| 3 | Lancaster County | 139,447 | 28 | Armstrong County | 47,641 | |
| 4 | Luzerne County | 133,065 | 38 | Beaver County | 39,605 | |
| 5 | Schuylkill County | 129,974 | 41 | Bedford County | 34,929 | |
| 6 | Berks County | 122,597 | 6 | Berks County | 122,597 | |
| 7 | Montgomery County | 96,494 | 25 | Blair County | 52,740 | |
| 8 | Lackawanna County | 89,269 | 19 | Bradford County | 58,541 | |
| 9 | York County | 87,841 | 15 | Bucks County | 68,656 | |
| 10 | Chester County | 83,481 | 26 | Butler County | 52,536 | |
| 11 | Westmoreland County | 78,036 | 29 | Cambria County | 46,811 | |
| 12 | Dauphin County | 76,148 | 66 | Cameron County | 5,159 | |
| 13 | Erie County | 74,688 | 48 | Carbon County | 31,923 | |
| 14 | Northampton County | 70,312 | 40 | Centre County | 37,922 | |
| 15 | Bucks County | 68,656 | 10 | Chester County | 83,481 | |
| 16 | Crawford County | 68,607 | 37 | Clarion County | 40,328 | |
| 17 | Lehigh County | 65,969 | 33 | Clearfield County | 43,408 | |
| 18 | Fayette County | 58,842 | 53 | Clinton County | 26,278 | |
| 19 | Bradford County | 58,541 | 47 | Columbia County | 32,409 | |
| 20 | Lycoming County | 57,486 | 16 | Crawford County | 68,607 | |
| 21 | Mercer County | 56,161 | 30 | Cumberland County | 45,977 | |
| 22 | Delaware County | 56,101 | 12 | Dauphin County | 76,148 | |
| 23 | Washington County | 55,418 | 22 | Delaware County | 56,101 | |
| 24 | Northumberland County | 53,123 | 62 | Elk County | 12,800 | |
| 25 | Blair County | 52,740 | 13 | Erie County | 74,688 | |
| 26 | Butler County | 52,536 | 18 | Fayette County | 58,842 | |
| 27 | Franklin County | 49,855 | 67 | Forest County | 4,385 | |
| 28 | Armstrong County | 47,641 | 27 | Franklin County | 49,855 | |
| 29 | Cambria County | 46,811 | 63 | Fulton County | 10,149 | |
| 30 | Cumberland County | 45,977 | 49 | Greene County | 28,273 | |
| 31 | Tioga County | 45,814 | 42 | Huntingdon County | 33,954 | |
| 32 | Venango County | 43,670 | 35 | Indiana County | 40,527 | |
| 33 | Clearfield County | 43,408 | 51 | Jefferson County | 27,935 | |
| 34 | McKean County | 42,565 | 56 | Juniata County | 18,227 | |
| 35 | Indiana County | 40,527 | 8 | Lackawanna County | 89,269 | |
| 36 | Susquehanna County | 40,354 | 3 | Lancaster County | 139,447 | |
| 37 | Clarion County | 40,328 | 44 | Lawrence County | 33,312 | |
| 38 | Beaver County | 39,605 | 39 | Lebanon County | 38,476 | |
| 39 | Lebanon County | 38,476 | 17 | Lehigh County | 65,969 | |
| 40 | Centre County | 37,922 | 4 | Luzerne County | 133,065 | |
| 41 | Bedford County | 34,929 | 20 | Lycoming County | 57,486 | |
| 42 | Huntingdon County | 33,954 | 34 | McKean County | 42,565 | |
| 43 | Wayne County | 33,513 | 21 | Mercer County | 56,161 | |
| 44 | Lawrence County | 33,312 | 55 | Mifflin County | 19,577 | |
| 45 | Somerset County | 33,110 | 54 | Monroe County | 20,175 | |
| 46 | Adams County | 32,455 | 7 | Montgomery County | 96,494 | |
| 47 | Columbia County | 32,409 | 60 | Montour County | 15,468 | |
| 48 | Carbon County | 31,923 | 14 | Northampton County | 70,312 | |
| 49 | Greene County | 28,273 | 24 | Northumberland County | 53,123 | |
| 50 | Warren County |