When people look at the United States, both geographically and in terms of population, they often break the figures into states, counties and congressional districts. This is among the ways that the Census Bureau “measures” America. According to Census Bureau data:

The United States total includes 3,006 counties; 14 boroughs and 11 census areas in Alaska; the District of Columbia; 64 parishes in Louisiana; Baltimore city, Maryland; St. Louis city, Missouri; that part of Yellowstone National Park in Montana; Carson City, Nevada; and 41 independent cities in Virginia.

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As would be expected, the largest counties contain America’s largest cities. For example, Maricopa, Arizona, the fourth-largest county by population, is home to Phoenix. Harris County, the third largest, is home to Houston.

24/7 Wall St. screened for America’s largest county by population, and found that of the 44 counties with populations exceeding 1 million, nine are in California, the most populous state. The biggest county in the country by population is Los Angeles County, which includes the city of Los Angeles, the nation’s second-biggest city.

To determine America’s largest county, 24/7 Wall St. reviewed five-year population data from the U.S. Census Bureau’s 2019 American Community Survey, ranking counties by population. For each county, we also collected land and total area in square miles, also from the Census Bureau, and calculated population density.

Though New York state is the fourth most populous, it has seven of the largest counties, and six of them have a population greater than 1 million. It is probably not surprising that four of them make up most of New York City: Queens, Kings, Bronx and New York counties.

Populations in the largest counties can be driven by economic opportunity, and many of the largest counties are also among the most affluent in their respective states, such as Arizona’s Maricopa County, Santa Clara County in California, North Carolina’s Wake County and Honolulu in Hawaii. In Fairfax County in Northern Virginia and Montgomery County in Maryland, both the population and household income have grown because of their proximity to Washington, D.C.

America’s largest county is Los Angeles, California. Here are the details:

• Population: 10,081,570
• Total area (including water) in square miles: 4,752.3 (95th highest)
• Land area square miles: 4,060.9 (116th highest)
• Population density: 2,466 (49th highest)

Click here to see all of America’s largest counties.

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