1840
| RANK | COUNTY | TOTAL POPULATION | RANK | COUNTY | TOTAL POPULATION | |
| 1 | Philadelphia County | 258,037 | 28 | Adams County | 23,044 | |
| 2 | Lancaster County | 84,203 | 3 | Allegheny County | 81,235 | |
| 3 | Allegheny County | 81,235 | 25 | Armstrong County | 28,365 | |
| 4 | Berks County | 64,569 | 22 | Beaver County | 29,368 | |
| 5 | Chester County | 57,515 | 23 | Bedford County | 29,335 | |
| 6 | Bucks County | 48,107 | 4 | Berks County | 64,569 | |
| 7 | Montgomery County | 47,241 | 17 | Bradford County | 32,769 | |
| 8 | York County | 47,010 | 6 | Bucks County | 48,107 | |
| 9 | Luzerne County | 44,006 | 31 | Butler County | 22,378 | |
| 10 | Westmoreland County | 42,699 | 45 | Cambria County | 11,256 | |
| 11 | Washington County | 41,279 | 35 | Centre County | 20,492 | |
| 12 | Northampton County | 40,996 | 5 | Chester County | 57,515 | |
| 13 | Franklin County | 37,793 | 50 | Clearfield County | 7,834 | |
| 14 | Huntingdon County | 35,484 | 49 | Clinton County | 8,323 | |
| 15 | Fayette County | 33,574 | 27 | Columbia County | 24,267 | |
| 16 | Mercer County | 32,873 | 18 | Crawford County | 31,724 | |
| 17 | Bradford County | 32,769 | 20 | Cumberland County | 30,953 | |
| 18 | Crawford County | 31,724 | 21 | Dauphin County | 30,118 | |
| 19 | Erie County | 31,344 | 37 | Delaware County | 19,791 | |
| 20 | Cumberland County | 30,953 | 19 | Erie County | 31,344 | |
| 21 | Dauphin County | 30,118 | 15 | Fayette County | 33,574 | |
| 22 | Beaver County | 29,368 | 13 | Franklin County | 37,793 | |
| 23 | Bedford County | 29,335 | 39 | Greene County | 19,147 | |
| 24 | Schuylkill County | 29,053 | 14 | Huntingdon County | 35,484 | |
| 25 | Armstrong County | 28,365 | 34 | Indiana County | 20,782 | |
| 26 | Lehigh County | 25,787 | 51 | Jefferson County | 7,253 | |
| 27 | Columbia County | 24,267 | 46 | Juniata County | 11,080 | |
| 28 | Adams County | 23,044 | 2 | Lancaster County | 84,203 | |
| 29 | Union County | 22,787 | 32 | Lebanon County | 21,872 | |
| 30 | Lycoming County | 22,649 | 26 | Lehigh County | 25,787 | |
| 31 | Butler County | 22,378 | 9 | Luzerne County | 44,006 | |
| 32 | Lebanon County | 21,872 | 30 | Lycoming County | 22,649 | |
| 33 | Susquehanna County | 21,195 | 54 | McKean County | 2,975 | |
| 34 | Indiana County | 20,782 | 16 | Mercer County | 32,873 | |
| 35 | Centre County | 20,492 | 43 | Mifflin County | 13,092 | |
| 36 | Northumberland County | 20,027 | 47 | Monroe County | 9,879 | |
| 37 | Delaware County | 19,791 | 7 | Montgomery County | 47,241 | |
| 38 | Somerset County | 19,650 | 12 | Northampton County | 40,996 | |
| 39 | Greene County | 19,147 | 36 | Northumberland County | 20,027 | |
| 40 | Venango County | 17,900 | 41 | Perry County | 17,096 | |
| 41 | Perry County | 17,096 | 1 | Philadelphia County | 258,037 | |
| 42 | Tioga County | 15,498 | 52 | Pike County | 3,832 | |
| 43 | Mifflin County | 13,092 | 53 | Potter County | 3,371 | |
| 44 | Wayne County | 11,848 | 24 | Schuylkill County | 29,053 | |
| 45 | Cambria County | 11,256 | 38 | Somerset County | 19,650 | |
| 46 | Juniata County | 11,080 | 33 | Susquehanna County | 21,195 | |
| 47 | Monroe County | 9,879 | 42 | Tioga County | 15,498 | |
| 48 | Warren County | 9,278 | 29 | Union County | 22,787 | |
| 49 | Clinton County | 8,323 | 40 | Venango County | 17,900 | |
| 50 | Clearfield County |