List of the most populous counties in the United States List of the most populous US counties sorted according to the mid-2011 official estimate by the USCB List of the most populous US counties sorted according to the mid-2011 official estimate by the USCB

| Rank_ | County | State_ | Land_area_km² | Land_area_mi² | April_1_2010_census | April_1_2010_density_km² | April_1_2010_density_mi² | July_1_2010_official_estimate | July_1_2010_density_km² | July_1_2010_density_mi² | July_1_2011_official_estimate | July_1_2011_density_km² | July_1_2011_density_mi² | Mid_2010_to_mid_2011_change_Absolute | Mid_2010_to_mid_2011_change_ | County_seat_or_courthouse |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 72 | Worcester County | Massachusetts | 3912.88 | 1510.77 | 798552 | 204 | 529 | 799300 | 204 | 529 | 801227 | 205 | 530 | 1927 | 0.24 | Worcester |
| 73 | Hamilton County | Ohio | 1051.30 | 405.91 | 802374 | 763 | 1977 | 801948 | 763 | 1976 | 800362 | 761 | 1972 | -1586 | -0.20 | Cincinnati |
| 74 | Hidalgo County | Texas | 4068.52 | 1570.87 | 774769 | 190 | 493 | 780030 | 192 | 497 | 797810 | 196 | 508 | 17780 | 2.28 | Edinburg |
| 75 | Essex County | New Jersey | 326.89 | 126.21 | 783969 | 2398 | 6211 | 784099 | 2399 | 6213 | 785137 | 2402 | 6221 | 1038 | 0.13 | Newark |
| 76 | Essex County | Massachusetts | 1275.73 | 492.56 | 743159 | 583 | 1509 | 744484 | 584 | 1511 | 748930 | 587 | 1520 | 4446 | 0.60 | Salem |
| 77 | Multnomah County | Oregon | 1117.05 | 431.30 | 735334 | 658 | 1705 | 737476 | 660 | 1710 | 748031 | 670 | 1734 | 10555 | 1.43 | Portland |