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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 96 | Davidson County | Tennessee | 1305.44 | 504.03 | 626681 | 480 | 1243 | 628053 | 481 | 1246 | 635475 | 487 | 1261 | 7422 | 1.18 | Nashville |
| 97 | Lee County | Florida | 2031.88 | 784.51 | 618754 | 305 | 789 | 620450 | 305 | 791 | 631330 | 311 | 805 | 10880 | 1.75 | Fort Myers |
| 98 | Monmouth County | New Jersey | 1214.17 | 468.79 | 630380 | 519 | 1345 | 630920 | 520 | 1346 | 631020 | 520 | 1346 | 100 | 0.02 | Freehold |
| 99 | Bucks County | Pennsylvania | 1565.15 | 604.31 | 625249 | 399 | 1035 | 625618 | 400 | 1035 | 626854 | 401 | 1037 | 1236 | 0.20 | Doylestown |
| 100 | Providence County | Rhode Island | 1060.60 | 409.50 | 626667 | 591 | 1530 | 626797 | 591 | 1531 | 626709 | 591 | 1530 | -88 | -0.01 | Providence |
| 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 |