1870
| RANK | COUNTY | TOTAL POPULATION | RANK | COUNTY | TOTAL POPULATION | |
| 1 | Philadelphia County | 674,022 | 39 | Adams County | 30,315 | |
| 2 | Allegheny County | 262,204 | 2 | Allegheny County | 262,204 | |
| 3 | Luzerne County | 160,915 | 24 | Armstrong County | 43,382 | |
| 4 | Lancaster County | 121,340 | 32 | Beaver County | 36,148 | |
| 5 | Schuylkill County | 116,428 | 40 | Bedford County | 29,635 | |
| 6 | Berks County | 106,701 | 6 | Berks County | 106,701 | |
| 7 | Montgomery County | 81,612 | 28 | Blair County | 38,051 | |
| 8 | Chester County | 77,805 | 17 | Bradford County | 53,204 | |
| 9 | York County | 76,134 | 11 | Bucks County | 64,336 | |
| 10 | Erie County | 65,973 | 31 | Butler County | 36,510 | |
| 11 | Bucks County | 64,336 | 30 | Cambria County | 36,569 | |
| 12 | Crawford County | 63,832 | 65 | Cameron County | 4,273 | |
| 13 | Northampton County | 61,432 | 43 | Carbon County | 28,144 | |
| 14 | Dauphin County | 60,740 | 35 | Centre County | 34,418 | |
| 15 | Westmoreland County | 58,719 | 8 | Chester County | 77,805 | |
| 16 | Lehigh County | 56,796 | 45 | Clarion County | 26,537 | |
| 17 | Bradford County | 53,204 | 47 | Clearfield County | 25,741 | |
| 18 | Mercer County | 49,977 | 50 | Clinton County | 23,211 | |
| 19 | Washington County | 48,483 | 41 | Columbia County | 28,766 | |
| 20 | Venango County | 47,925 | 12 | Crawford County | 63,832 | |
| 21 | Lycoming County | 47,626 | 23 | Cumberland County | 43,912 | |
| 22 | Franklin County | 45,365 | 14 | Dauphin County | 60,740 | |
| 23 | Cumberland County | 43,912 | 27 | Delaware County | 39,403 | |
| 24 | Armstrong County | 43,382 | 62 | Elk County | 8,488 | |
| 25 | Fayette County | 43,284 | 10 | Erie County | 65,973 | |
| 26 | Northumberland County | 41,444 | 25 | Fayette County | 43,284 | |
| 27 | Delaware County | 39,403 | 66 | Forest County | 4,010 | |
| 28 | Blair County | 38,051 | 22 | Franklin County | 45,365 | |
| 29 | Susquehanna County | 37,523 | 60 | Fulton County | 9,360 | |
| 30 | Cambria County | 36,569 | 46 | Greene County | 25,887 | |
| 31 | Butler County | 36,510 | 38 | Huntingdon County | 31,251 | |
| 32 | Beaver County | 36,148 | 33 | Indiana County | 36,138 | |
| 33 | Indiana County | 36,138 | 51 | Jefferson County | 21,656 | |
| 34 | Tioga County | 35,097 | 54 | Juniata County | 17,390 | |
| 35 | Centre County | 34,418 | 4 | Lancaster County | 121,340 | |
| 36 | Lebanon County | 34,096 | 44 | Lawrence County | 27,298 | |
| 37 | Wayne County | 33,188 | 36 | Lebanon County | 34,096 | |
| 38 | Huntingdon County | 31,251 | 16 | Lehigh County | 56,796 | |
| 39 | Adams County | 30,315 | 3 | Luzerne County | 160,915 | |
| 40 | Bedford County | 29,635 | 21 | Lycoming County | 47,626 | |
| 41 | Columbia County | 28,766 | 61 | McKean County | 8,825 | |
| 42 | Somerset County | 28,226 | 18 | Mercer County | 49,977 | |
| 43 | Carbon County | 28,144 | 53 | Mifflin County | 17,508 | |
| 44 | Lawrence County | 27,298 | 52 | Monroe County | 18,362 | |
| 45 | Clarion County | 26,537 | 7 | Montgomery County | 81,612 | |
| 46 | Greene County | 25,887 | 57 | Montour County | 15,344 | |
| 47 | Clearfield County | 25,741 | 13 | Northampton County | 61,432 | |
| 48 | Perry County | 25,447 | 26 | Northumberland County | 41,444 | |
| 49 | Warren County | 23,897 | 48 | Perry County | 25,447 | |
| 50 | Clinton County |