| Rank
| County
| Population
| County Seat or Courthouse
|
| 1
| Los Angeles County, California
| 9,937,739
| Los Angeles
|
| 2
| Cook County, Illinois
| 5,327,777
| Chicago
|
| 3
| Harris County, Texas
| 3,644,285
| Houston
|
| 4
| Maricopa County, Arizona
| 3,501,001
| Phoenix
|
| 5
| Orange County, California
| 2,987,591
| Santa Ana
|
| 6
| San Diego County, California
| 2,931,714
| San Diego
|
| 7
| Kings County, New York
| 2,475,290
| Brooklyn
|
| 8
| Miami-Dade County, Florida
| 2,363,600
| Miami
|
| 9
| Dallas County, Texas
| 2,294,706
| Dallas
|
| 10
| Queens County, New York
| 2,237,216
| Jamaica
|
| 11
| Wayne County, Michigan
| 2,016,202
| Detroit
|
| 12
| San Bernardino County, California
| 1,921,131
| San Bernardino
|
| 13
| Riverside County, California
| 1,871,950
| Riverside
|
| 14
| King County, Washington
| 1,777,143
| Seattle
|
| 15
| Broward County, Florida
| 1,754,893
| Fort Lauderdale
|
| 16
| Santa Clara County, California
| 1,685,188
| San Jose
|
| 17
| Clark County, Nevada
| 1,650,671
| Las Vegas
|
| 18
| Tarrant County, Texas
| 1,588,088
| Fort Worth
|
| 19
| New York County, New York
| 1,562,723
| New York
|
| 20
| Bexar County, Texas
| 1,493,965
| San Antonio
|
| 21
| Suffolk County, New York
| 1,475,488
| Riverhead
|
| 22
| Philadelphia County, Pennsylvania
| 1,470,151
| Philadelphia
|
| 23
| Middlesex County, Massachusetts
| 1,464,628
| Cambridge
|
| 24
| Alameda County, California
| 1,455,235
| Oakland
|
| 25
| Cuyahoga County, Ohio
| 1,365,536
| Cleveland
|
| 26
| Bronx County, New York
| 1,363,198
| The Bronx
|
| 27
| Nassau County, New York
| 1,339,463
| Mineola
|
| 28
| Sacramento County, California
| 1,330,711
| Sacramento
|
| 29
| Allegheny County, Pennsylvania
| 1,261,303
| Pittsburgh
|
| 30
| Palm Beach County, Florida
| 1,216,282
| West Palm Beach
|
| 31
| Oakland County, Michigan
| 1,207,869
| Pontiac
|
| 32
| Hennepin County, Minnesota
| 1,121,035
| Minneapolis
|
| 33
| Franklin County, Ohio
| 1,088,944
| Columbus
|
| 34
| Hillsborough County, Florida
| 1,073,407
| Tampa
|
| 35
| Saint Louis County, Missouri
| 1,013,123
| Clayton
|
| 36
| Contra Costa County, California
| 1,001,136
| Martinez
|
| 37
| Fairfax County, Virginia
| 1,000,405
| Fairfax
|
| 38
| Orange County, Florida
| 964,865
| Orlando
|
| 39
| Erie County, New York
| 941,293
| Buffalo
|
| 40
| Westchester County, New York
| 940,302
| White Plains
|
| 41
| Milwaukee County, Wisconsin
| 933,221
| Milwaukee
|
| 42
| Pinellas County, Florida
| 926,146
| Clearwater
|
| 43
| DuPage County, Illinois
| 925,188
| Wheaton
|
| 44
| Salt Lake County, Utah
| 924,247
| Salt Lake City
|
| 45
| Montgomery County, Maryland
| 918,881
| Rockville
|
| 46
| Shelby County, Tennessee
| 906,178
| Memphis
|
| 47
| Honolulu County, Hawaii
| 902,704
| Honolulu
|
| 48
| Fairfield County, Connecticut
| 899,152
| Bridgeport
|
| 49
| Bergen County, New Jersey
| 897,569
| Hackensack
|
| 50
| Pima County, Arizona
| 892,798
| Tucson
|
| 51
| Hartford County, Connecticut
| 871,457
| Hartford
|
| 52
| Marion County, Indiana
| 863,251
| Indianapolis
|
| 53
| Travis County, Texas
| 857,204
| Austin
|
| 54
| Fresno County, California
| 850,325
| Fresno
|
| 55
| New Haven County, Connecticut
| 841,873
| New Haven
|
| 56
| Prince George's County, Maryland
| 838,716
| Upper Marlboro
|
| 57
| Hamilton County, Ohio
| 823,742
| Cincinnati
|
| 58
| Fulton County, Georgia
| 818,322
| Atlanta
|
| 59
| Duval County, Florida
| 817,480
| Jacksonville
|
| 60
| Macomb County, Michigan
| 813,948
| Mount Clemens
|
| 61
| Essex County, New Jersey
| 796,313
| Newark
|
| 62
| Ventura County, California
| 791,130
| Ventura
|
| 63
| Middlesex County, New Jersey
| 780,995
| New Brunswick
|
| 64
| Baltimore County, Maryland
| 777,184
| Towson
|
| 65
| Worcester County, Massachusetts
| 776,610
| Worcester
|
| 66
| Montgomery County, Pennsylvania
| 770,747
| Norristown
|
| 67
| Mecklenburg County, North Carolina
| 752,366
| Charlotte
|
| 68
| San Francisco County, California
| 751,682
| San Francisco
|
| 69
| Pierce County, Washington
| 740,957
| Tacoma
|
| 70
| Essex County, Massachusetts
| 737,848
| Salem
|
| 71
| Monroe County, New York
| 736,738
| Rochester
|
| 72
| Kern County, California
| 713,087
| Bakersfield
|
| 73
| El Paso County, Texas
| 705,436
| El Paso
|
| 74
| Jefferson County, Kentucky
| 699,017
| Louisville
|
| 75
| San Mateo County, California
| 697,456
| Redwood City
|
| 76
| Wake County, North Carolina
| 695,681
| Raleigh
|
| 77
| Lake County, Illinois
| 685,019
| Waukegan
|
| 78
| Suffolk County, Massachusetts
| 680,705
| Boston
|
| 79
| Multnomah County, Oregon
| 677,813
| Portland
|
| 80
| Oklahoma County, Oklahoma
| 676,066
| Oklahoma City
|
| 81
| DeKalb County, Georgia
| 674,334
| Decatur
|
| 82
| Gwinnett County, Georgia
| 673,345
| Lawrenceville
|
| 83
| Jackson County, Missouri
| 659,723
| Independence
|
| 84
| Jefferson County, Alabama
| 658,141
| Birmingham
|
| 85
| Norfolk County, Massachusetts
| 654,331
| Dedham
|
| 86
| Cobb County, Georgia
| 651,027
| Marietta
|
| 87
| Providence County, Rhode Island
| 639,442
| Providence
|
| 88
| Snohomish County, Washington
| 639,409
| Everett
|
| 89
| Hidalgo County, Texas
| 635,540
| Edinburg
|
| 90
| San Joaquin County, California
| 632,760
| Stockton
|
| 91
| Monmouth County, New Jersey
| 632,274
| Freehold Borough
|
| 92
| Bucks County, Pennsylvania
| 613,110
| Doylestown
|
| 93
| Hudson County, New Jersey
| 607,419
| Jersey City
|
| 94
| Collin County, Texas
| 597,147
| McKinney
|
| 95
| Kent County, Michigan
| 590,417
| Grand Rapids
|
| 96
| Will County, Illinois
| 586,706
| Joliet
|
| 97
| Bernalillo County, New Mexico
| 581,442
| Albuquerque
|
| 98
| Tulsa County, Oklahoma
| 570,313
| Tulsa
|
| 99
| Davidson County, Tennessee
| 569,842
| Nashville
|
| 100
| Denver County, Colorado
| 557,478
| Denver
|
"List of the most populous counties in the United States".