Table 1.  The Most Populous Counties and the Most Populous Cities and Townships in 2010 in Pennsylvania:  2000 and 2010
(For information on confidentiality protection, nonsampling error, and definitions, see http://www.census.gov/prod/cen2010/pl94-171.pdf)
Population rank     Population Change, 2000 to 2010
             
2010 2000   Geographic area 2000 1 2010 Number Percent
             
    Pennsylvania…...………………………………………………. 12 281 054 12 702 379  421 325 3.4
             
    COUNTY        
             
1 1   Philadelphia County 2…………………………………….. 1 517 550 1 526 006  8 456 0.6
2 2   Allegheny County………………………………………….. 1 281 666 1 223 348 - 58 318 -4.6
3 3   Montgomery County…………………………………………  750 097  799 874  49 777 6.6
4 4   Bucks County……………………………………..………….  597 635  625 249  27 614 4.6
5 5   Delaware County………………………………………….  550 864  558 979  8 115 1.5
6 6   Lancaster County…………………………………………  470 658  519 445  48 787 10.4
7 7   Chester County……………………………………………  433 501  498 886  65 385 15.1
8 8   York County…………………………………………………  381 751  434 972  53 221 13.9
9 9   Berks County………………………………………..………..  373 638  411 442  37 804 10.1
10 10   Westmoreland County………………………………………  369 993  365 169 - 4 824 -1.3
11 12   Lehigh County……………………………………………..  312 090  349 497  37 407 12.0
12 11   Luzerne County……………………………………………….  319 250  320 918  1 668 0.5
13 14   Northampton County………………………………………..  267 066  297 735  30 669 11.5
14 13   Erie County…………………………………………………..  280 843  280 566 -  277 -0.1
15 15   Dauphin County……………………………………………..  251 798  268 100  16 302 6.5
16 16   Cumberland County……………………………………………  213 674  235 406  21 732 10.2
17 17   Lackawanna County…………………………………………  213 295  214 437  1 142 0.5
18 18   Washington County…………………………..…………………  202 897  207 820  4 923 2.4
19 20   Butler County………………………………………………  174 083  183 862  9 779 5.6
20 19   Beaver County……………………………………………….  181 412  170 539 - 10 873 -6.0
             
    CITY OR TOWNSHIP        
             
1 1   Philadelphia city 2…………………………………..………. 1 517 550 1 526 006  8 456 0.6
2 2   Pittsburgh city………………………………………..………  334 563  305 704 - 28 859 -8.6
3 3   Allentown city………………………………………..…………  106 632  118 032  11 400 10.7
4 4   Erie city………………………………………………...………..  103 717  101 786 - 1 931 -1.9
5 6   Reading city………………………………………...……………  81 207  88 082  6 875 8.5
6 5   Upper Darby township (Delaware County)………………..  81 821  82 795   974 1.2
7 7   Scranton city……………………………………….…………..  76 415  76 089 -  326 -0.4
8 8   Bethlehem city…………………………………………….  71 329  74 982  3 653 5.1
9 10   Bensalem township (Bucks County)…………..……………  58 434  60 427  1 993 3.4
10 11   Lancaster city……………………………………………...……  56 348  59 322  2 974 5.3
11 9   Lower Merion township (Montgomery County)………….  59 850  57 825 - 2 025 -3.4
12 12   Abington township (Montgomery County)……………..  56 103  55 310 -  793 -1.4
13 13   Bristol township (Bucks County)………………………………  55 521  54 582 -  939 -1.7
14 14   Millcreek township (Erie County)………………………………  52 129  53 515  1 386 2.7
15 16   Harrisburg city……………………………………………...……..  48 950  49 528   578 1.2
16 17   Haverford township (Delaware County)………………………..  48 498  48 491 -  7 -
17 19   Lower Paxton township (Dauphin County)…………………….  44 424  47 360  2 936 6.6
18 15   Altoona city…………………………………………………..  49 523  46 320 - 3 203 -6.5
19 20   Middletown township (Bucks County)………………………..  44 141  45 436  1 295 2.9
20 22   York city………………………………………………………  40 862  43 718  2 856 7.0
               
 -  Represents zero or rounds to 0.0.
1 Census 2000 counts are as published in Census 2000 reports and thus do not include any changes published subsequently due to boundary changes or to the Count Question Resolution program.
2 Philadelphia County and Philadelphia city are coextensive.
Source:  U.S. Census Bureau, Census 2000 Redistricting Data (Public Law 94-171) Summary File, Table PL1, and 2010 Census Redistricting Data (Public Law 94-171) Summary File, Table P1.