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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 48 | Fresno County | California | 15431.13 | 5957.99 | 930450 | 60 | 156 | 933168 | 60 | 157 | 942904 | 61 | 158 | 9736 | 1.04 | Fresno |
| 49 | Shelby County | Tennessee | 1976.61 | 763.17 | 927644 | 469 | 1216 | 928930 | 470 | 1217 | 935088 | 473 | 1225 | 6158 | 0.66 | Memphis |
| 50 | Wake County | North Carolina | 2163.21 | 835.22 | 900993 | 417 | 1079 | 906788 | 419 | 1086 | 929780 | 430 | 1113 | 22992 | 2.54 | Raleigh |
| 51 | Fairfield County | Connecticut | 1618.46 | 624.89 | 916829 | 566 | 1467 | 918339 | 567 | 1470 | 925899 | 572 | 1482 | 7560 | 0.82 | Bridgeport |
| 52 | DuPage County | Illinois | 848.22 | 327.50 | 916924 | 1081 | 2800 | 917942 | 1082 | 2803 | 923222 | 1088 | 2819 | 5280 | 0.58 | Wheaton |
| 53 | Erie County | New York | 2700.56 | 1042.69 | 919040 | 340 | 881 | 918751 | 340 | 881 | 918028 | 340 | 880 | -723 | -0.08 | Buffalo |