This list includes the most populous US counties by population estimates by the United States Census Bureau (USCB).
| Rank | County | State | Land area | July 1, 2023 estimates | County seat | |
|---|---|---|---|---|---|---|
| km2[5] | mi2[6] | |||||
| 1 | Los Angeles | California | 10,509.87 | 4,057.88 | 9,663,345 | Los Angeles |
| 2 | Cook | Illinois | 2,448.38 | 945.33 | 5,087,072 | Chicago |
| 3 | Harris | Texas | 4,411.99 | 1,703.48 | 4,835,125 | Houston |
| 4 | Maricopa | Arizona | 23,828.26 | 9,200.14 | 4,585,871 | Phoenix |
| 5 | San Diego | California | 10,895.12 | 4,206.63 | 3,269,973 | San Diego |
| 6 | Orange | 2,047.56 | 790.57 | 3,135,755 | Santa Ana | |
| 7 | Miami-Dade | Florida | 4,915.06 | 1,897.72 | 2,686,867 | Miami |
| 8 | Dallas | Texas | 2,256.60 | 871.28 | 2,606,358 | Dallas |
| 9 | Kings | New York | 183.41 | 70.82 | 2,561,225 | Brooklyn, NYC |
| 10 | Riverside | California | 18,664.70 | 7,206.48 | 2,492,442 | Riverside |
| 11 | Clark | Nevada | 20,438.71 | 7,891.43 | 2,336,573 | Las Vegas |
| 12 | King | Washington | 5,479.29 | 2,115.57 | 2,271,380 | Seattle |
| 13 | Queens | New York | 281.10 | 108.53 | 2,252,196 | Queens, NYC |
| 14 | San Bernardino | California | 51,947.23 | 20,056.94 | 2,195,611 | San Bernardino |
| 15 | Tarrant | Texas | 2,236.74 | 863.61 | 2,182,947 | Fort Worth |
| 16 | Bexar | 3,211.12 | 1,239.82 | 2,087,679 | San Antonio | |
| 17 | Broward | Florida | 3,133.33 | 1,209.79 | 1,962,531 | Fort Lauderdale |
| 18 | Santa Clara | California | 3,341.34 | 1,290.10 | 1,877,592 | San Jose |
| 19 | Wayne | Michigan | 1,585.28 | 612.08 | 1,751,169 | Detroit |
| 20 | Middlesex | Massachusetts | 2,118.14 | 817.82 | 1,623,952 | Lowell and Cambridge |
| 21 | Alameda | California | 1,914.05 | 739.02 | 1,622,188 | Oakland |
| 22 | New York | New York | 59.13 | 22.83 | 1,597,451 | Manhattan, NYC |
| 23 | Sacramento | California | 2,498.42 | 964.64 | 1,584,288 | Sacramento |
| 24 | Philadelphia | Pennsylvania | 347.32 | 134.10 | 1,550,542 | Philadelphia |
| 25 | Hillsborough | Florida | 2,642.34 | 1,020.21 | 1,535,564 | Tampa |
| 26 | Palm Beach | 5,100.00 | 1,970.00 | 1,533,801 | West Palm Beach | |
| 27 | Suffolk | New York | 2,362.20 | 912.05 | 1,523,170 | Riverhead |
| 28 | Orange | Florida | 2,339.87 | 903.43 | 1,471,416 | Orlando |
| 29 | Nassau | New York | 737.41 | 284.72 | 1,381,715 | Mineola |
| 30 | Bronx | 109.03 | 42.10 | 1,356,476 | Bronx, NYC | |
| 31 | Travis | Texas | 2,564.61 | 990.20 | 1,334,961 | Austin |
| 32 | Franklin | Ohio | 1,378.36 | 532.19 | 1,326,063 | Columbus |
| 33 | Oakland | Michigan | 2,247.24 | 867.66 | 1,270,426 | Pontiac |
| 34 | Hennepin | Minnesota | 1,433.79 | 553.59 | 1,258,713 | Minneapolis |
| 35 | Cuyahoga | Ohio | 1,184.12 | 457.19 | 1,233,088 | Cleveland |
| 36 | Allegheny | Pennsylvania | 1,890.88 | 730.07 | 1,224,825 | Pittsburgh |
| 37 | Collin | Texas | 2,178.76 | 841.22 | 1,195,359 | McKinney |
| 38 | Wake | North Carolina | 2,163.21 | 835.22 | 1,190,275 | Raleigh |
| 39 | Salt Lake | Utah | 1,922.50 | 742.28 | 1,185,813 | Salt Lake City |
| 40 | Mecklenburg | North Carolina | 1,356.75 | 523.84 | 1,163,701 | Charlotte |
| 41 | Contra Costa | California | 1,854.27 | 715.94 | 1,155,025 | Martinez |
| 42 | Fairfax | Virginia | 1,012.60 | 390.97 | 1,141,878 | Fairfax |
| 43 | Fulton | Georgia | 1,363.98 | 526.63 | 1,079,105 | Atlanta |
| 44 | Pima | Arizona | 23,794.31 | 9,187.04 | 1,063,162 | Tucson |
| 45 | Montgomery | Maryland | 1,272.34 | 491.25 | 1,058,474 | Rockville |
| 46 | Duval | Florida | 1,974.07 | 762.19 | 1,030,822 | Jacksonville |
| 47 | Fresno | California | 15,431.13 | 5,957.99 | 1,017,162 | Fresno |
| 48 | Denton | Texas | 2,275.13 | 878.43 | 1,007,703 | Denton |
| 49 | Westchester | New York | 1,114.98 | 430.50 | 990,817 | White Plains |
| 50 | Honolulu | Hawaii | 1,555.92 | 600.74 | 989,408 | Honolulu |
| 51 | St. Louis | Missouri | 1,315.20 | 507.80 | 987,059 | Clayton |
| 52 | Gwinnett | Georgia | 1,114.69 | 430.38 | 983,526 | Lawrenceville |
| 53 | Capitol | Connecticut | 2,660.80 | 1,027.34 | 975,328 | Hartford |
| 54 | Marion | Indiana | 1,026.41 | 396.30 | 968,460 | Indianapolis |
| 55 | Pinellas | Florida | 709.14 | 273.80 | 961,596 | Clearwater |
| 56 | Bergen | New Jersey | 603.49 | 233.01 | 957,736 | Hackensack |
| 57 | Prince George's | Maryland | 1,250.16 | 482.69 | 947,430 | Upper Marlboro |
| 58 | Erie | New York | 2,700.56 | 1,042.69 | 946,147 | Buffalo |
| 59 | Pierce | Washington | 4,324.01 | 1,669.51 | 928,696 | Tacoma |
| 60 | DuPage | Illinois | 848.22 | 327.50 | 921,213 | Wheaton |
| 61 | Fort Bend | Texas | 2,292 | 885 | 916,778 | Richmond |
| 62 | Milwaukee | Wisconsin | 625.23 | 241.40 | 916,205 | Milwaukee |
| 63 | Kern | California | 21,061.57 | 8,131.92 | 913,820 | Bakersfield |
| 64 | Shelby | Tennessee | 1,976.61 | 763.17 | 910,042 | Memphis |
| 65 | Hidalgo | Texas | 4,068.52 | 1,570.87 | 898,471 | Edinburg |
| 66 | Macomb | Michigan | 1,241.18 | 479.22 | 875,101 | Mount Clemens |
| 67 | El Paso | Texas | 2,622.86 | 1,012.69 | 869,880 | El Paso |
| 68 | Montgomery | Pennsylvania | 1,251.07 | 483.04 | 868,742 | Norristown |
| 69 | Worcester | Massachusetts | 3,912.88 | 1,510.77 | 866,866 | Worcester |
| 70 | Middlesex | New Jersey | 800.08 | 308.91 | 863,623 | New Brunswick |
| 71 | Essex | 326.89 | 126.21 | 851,117 | Newark | |
| 72 | Snohomish | Washington | 5,406.01 | 2,087.27 | 844,761 | Everett |
| 73 | Baltimore | Maryland | 1,549.59 | 598.30 | 844,703 | Towson |
| 74 | Lee | Florida | 2,031.88 | 784.51 | 834,573 | Fort Myers |
| 75 | Ventura | California | 4,773.69 | 1,843.13 | 829,590 | Ventura |
| 76 | Hamilton | Ohio | 1,051.30 | 405.91 | 827,058 | Cincinnati |
| 77 | Polk | Florida | 4,660 | 1,798 | 818,330 | Bartow |
| 78 | Essex | Massachusetts | 1,275.73 | 492.56 | 810,089 | Salem and Lawrence |
| 79 | San Francisco | California | 121.40 | 46.87 | 808,988 | San Francisco |
| 80 | Oklahoma | Oklahoma | 1,835.83 | 708.82 | 808,866 | Oklahoma City |
| 81 | San Joaquin | California | 3,603.51 | 1,391.32 | 800,965 | Stockton |
| 82 | Multnomah | Oregon | 1,117.05 | 431.30 | 789,698 | Portland |
| 83 | Cobb | Georgia | 879.43 | 339.55 | 776,743 | Marietta |
| 84 | Jefferson | Kentucky | 985.27 | 380.42 | 772,144 | Louisville |
| 85 | Suffolk | Massachusetts | 150.62 | 58.15 | 768,425 | Boston |
| 86 | DeKalb | Georgia | 693.03 | 267.58 | 762,992 | Decatur |
| 87 | Monroe | New York | 1,702.15 | 657.21 | 748,482 | Rochester |
| 88 | El Paso | Colorado | 5,508.39 | 2,126.80 | 744,215 | Colorado Springs |
| 89 | Norfolk | Massachusetts | 1,025.91 | 396.11 | 727,473 | Dedham |
| 90 | San Mateo | California | 1,161.37 | 448.41 | 726,353 | Redwood City |
| 91 | Utah | Utah | 5,188.91 | 2,003.45 | 719,174 | Provo |
| 92 | Jackson | Missouri | 1,565.55 | 604.46 | 718,560 | Independence and Kansas City |
| 93 | Denver | Colorado | 401.36 | 154.97 | 716,577 | Denver |
| 94 | Davidson | Tennessee | 1,305.44 | 504.03 | 712,334 | Nashville |
| 95 | Montgomery | Texas | 2,699.23 | 1,042.18 | 711,354 | Conroe |
| 96 | Lake | Illinois | 1,149.10 | 443.67 | 708,760 | Waukegan |
| 97 | Hudson | New Jersey | 119.63 | 46.19 | 705,472 | Jersey City |
| 98 | Will | Illinois | 2,167.58 | 836.91 | 700,728 | Joliet |
| 99 | Williamson | Texas | 2,889.99 | 1,115.83 | 697,191 | Georgetown |
| 100 | Tulsa | Oklahoma | 1,476.86 | 570.22 | 682,868 | Tulsa |