| Rank
| County
| Population
| County Seat or Courthouse
| Total Area (Square Miles/km}
|
| 1
| Los Angeles County, California
| 9,948,081
| Los Angeles
| 4,752 sq mi/12,308 km²
|
| 2
| Cook County, Illinois
| 5,288,655
| Chicago
| 1,635 sq mi/4,235 km²
|
| 3
| Harris County, Texas
| 3,886,207
| Houston
| 1,778 sq mi/4,605 km²
|
| 4
| Maricopa County, Arizona
| 3,768,123
| Phoenix
| 9,224 sq mi/23,890 km²
|
| 5
| Orange County, California
| 3,002,048
| Santa Ana
| 948 sq mi/2,455 km²
|
| 6
| San Diego County, California
| 2,941,454
| San Diego
| 4,526 sq mi/11,722 km²
|
| 7
| Kings County, New York
| 2,508,820
| Brooklyn
| 96.90 sq mi/251 km²
|
| 8
| Miami-Dade County, Florida
| 2,402,208
| Miami
| 2,431 sq mi/6,296 km²
|
| 9
| Dallas County, Texas
| 2,345,815
| Dallas
| 908 sq mi/2,353 km²
|
| 10
| Queens County, New York
| 2,255,175
| Queens
| 178.28 sq mi/461.74 km²
|
| 11
| Riverside County, California
| 2,026,803
| Riverside
|
| 12
| San Bernardino County, California
| 1,999,332
| San Bernardino
|
| 13
| Wayne County, Michigan
| 1,946,419
| Detroit
|
| 14
| King County, Washington
| 1,826,732
| Seattle
|
| 15
| Broward County, Florida
| 1,787,636
| Fort Lauderdale
|
| 16
| Clark County, Nevada
| 1,777,539
| Las Vegas
|
| 17
| Santa Clara County, California
| 1,731,281
| San Jose
|
| 18
| Tarrant County, Texas
| 1,671,295
| Fort Worth
|
| 19
| New York County, New York
| 1,611,581
| New York
|
| 20
| Bexar County, Texas
| 1,555,592
| San Antonio
|
| 21
| Suffolk County, New York
| 1,469,715
| Riverhead
|
| 22
| Middlesex County, Massachusetts
| 1,467,016
| Cambridge
|
| 23
| Alameda County, California
| 1,457,426
| Oakland
|
| 24
| Philadelphia County, Pennsylvania
| 1,448,905
| Philadelphia
|
| 25
| Sacramento County, California
| 1,374,724
| Sacramento
|
| 26
| Bronx County, New York
| 1,361,473
| The Bronx
|
| 27
| Nassau County, New York
| 1,325,662
| Mineola
|
| 28
| Cuyahoga County, Ohio
| 1,314,241
| Cleveland
|
| 29
| Palm Beach County, Florida
| 1,274,013
| West Palm Beach
|
| 30
| Allegheny County, Pennsylvania
| 1,223,411
| Pittsburgh
|
| 31
| Oakland County, Michigan
| 1,214,255
| Pontiac
|
| 32
| Hillsborough County, Florida
| 1,157,738
| Tampa
|
| 33
| Hennepin County, Minnesota
| 1,122,093
| Minneapolis
|
| 34
| Franklin County, Ohio
| 1,095,662
| Columbus
|
| 35
| Orange County, Florida
| 1,043,500
| Orlando
|
| 36
| Contra Costa County, California
| 1,024,319
| Martinez
|
| 37
| Fairfax County, Virginia
| 1,010,443
| Fairfax
|
| 38
| Saint Louis County, Missouri
| 1,000,510
| Clayton
|
| 39
| Salt Lake County, Utah
| 978,701
| Salt Lake City
|
| 40
| Fulton County, Georgia
| 960,009
| Atlanta
|
| 41
| Westchester County, New York
| 949,355
| White Plains
|
| 42
| Pima County, Arizona
| 946,362
| Tucson
|
| 43
| DuPage County, Illinois
| 932,670
| Wheaton
|
| 44
| Montgomery County, Maryland
| 932,131
| Rockville
|
| 45
| Pinellas County, Florida
| 924,413
| Clearwater
|
| 46
| Erie County, New York
| 921,390
| Buffalo
|
| 47
| Travis County, Texas
| 921,006
| Austin
|
| 48
| Milwaukee County, Wisconsin
| 915,097
| Milwaukee
|
| 50
| Honolulu County, Hawaii
| 909,863
| Honolulu
|
| 51
| Shelby County, Tennessee
| 905,266
| Memphis
|
| 52
| Bergen County, New Jersey
| 904,037
| Hackensack
|
| 53
| Fairfield County, Connecticut
| 900,440
| Bridgeport
|
| 54
| Fresno County, California
| 891,756
| Fresno
|
| 55
| Hartford County, Connecticut
| 876,927
| Hartford
|
| 56
| Marion County, Indiana
| 865,504
| Indianapolis
|
| 57
| New Haven County, Connecticut
| 845,244
| New Haven
|
| 58
| Prince George's County, Maryland
| 841,315
| Upper Marlboro
|
| 59
| Duval County, Florida
| 837,964
| Jacksonville
|
| 60
| Macomb County, Michigan
| 832,861
| Mount Clemens
|
| 61
| Mecklenburg County, North Carolina
| 827,445
| Charlotte
|
| 62
| Hamilton County, Ohio
| 822,596
| Cincinnati
|
| 63
| Ventura County, California
| 799,720
| Ventura
|
| 64
| Essex County, New Jersey
| 791,057
| Newark
|
| 65
| Middlesex County, New Jersey
| 789,516
| New Brunswick
|
| 66
| Baltimore County, Maryland
| 787,384
| Towson
|
| 67
| Wake County, North Carolina
| 786,522
| Raleigh
|
| 68
| Worcester County, Massachusetts
| 784,992
| Worcester
|
| 69
| Kern County, California
| 780,117
| Bakersfield
|
| 70
| Montgomery County, Pennsylvania
| 775,688
| Norristown
|
| 71
| Pierce County, Washington
| 766,878
| Tacoma
|
| 72
| Gwinnett County, Georgia
| 757,104
| Lawrenceville
|
| 73
| San Francisco County, California
| 744,041
| San Francisco
|
| 74
| El Paso County, Texas
| 736,310
| El Paso
|
| 75
| Essex County, Massachusetts
| 735,958
| Salem
|
| 76
| Monroe County, New York
| 730,807
| Rochester
|
| 77
| DeKalb County, Georgia
| 723,602
| Decatur
|
| 78
| Lake County, Illinois
| 713,076
| Waukegan
|
| 79
| San Mateo County, California
| 705,499
| Redwood City
|
| 80
| Jefferson County, Kentucky
| 701,500
| Louisville
|
| 81
| Hidalgo County, Texas
| 700,634
| Edinburg
|
| 82
| Collin County, Texas
| 698,851
| McKinney
|
| 83
| Oklahoma County, Oklahoma
| 691,266
| Oklahoma City
|
| 84
| Suffolk County, Massachusetts
| 687,610
| Boston
|
| 85
| Multnomah County, Oregon
| 681,454
| Portland
|
| 86
| Cobb County, Georgia
| 679,325
| Marietta
|
| 87
| San Joaquin County, California
| 673,170
| Stockton
|
| 88
| Snohomish County, Washington
| 669,887
| Everett
|
| 89
| Will County, Illinois
| 668,217
| Joliet
|
| 90
| Jackson County, Missouri
| 664,078
| Independence
|
| 91
| Jefferson County, Alabama
| 656,700
| Birmingham
|
| 92
| Norfolk County, Massachusetts
| 654,753
| Dedham
|
| 93
| Providence County, Rhode Island
| 635,596
| Providence
|
| 94
| Monmouth County, New Jersey
| 635,285
| Freehold Borough
|
| 95
| Baltimore City
| 631,366
| Baltimore
|
| 96
| Bucks County, Pennsylvania
| 623,205
| Doylestown
|
| 97
| Bernalillo County, New Mexico
| 615,099
| Albuquerque
|
| 98
| Davidson County, Tennessee
| 607,413
| Nashville
|
| 99
| Hudson County, New Jersey
| 601,146
| Jersey City
|
| 100
| Kent County, Michigan
| 599,524
| Grand Rapids
|
