The 25 Largest Counties in the United States

There is no doubt that the United States of America is one of the most popular tourist attractions in the world, as it is also one of the leading innovators in entertainment, science, and technology.

There are approximately 329.5 million people living in the Land of Opportunity across 50 states and 3,143 counties.

The most populated U.S. state is California, with about 39.2 million residents living in its 155,959 sq mi area.

In fact, Los Angeles County is California’s largest county and the largest county by population in the United States, with 10,014,009 people living here.

The second largest county by population is Cook County, Illinois with 5,275,541 residents, followed by the third largest Harris County, Texas with 4,731,145 residents.

To see the complete ranking, this article includes the top 25 largest counties in the United States by population.

Table of Contents

1. Los Angeles County, California – 10,014,009

Los Angeles
Chones / Shutterstock

Total Area: 4,751 sq mi or 12,310 km2

Population Density: 2,430/sq mi

Los Angeles County is the most populated county in the United States, with a total population of 10,014,009 residents.

It is estimated that 3,898,747 people live in the city of Los Angeles, making it the largest city in Los Angeles County.

The county is best known as an entertainment center that is home to five major film studios and many tourist attractions including the most visited park Griffith Park, Venice Beach, and amusement parks.

2. Cook County, Illinois – 5,275,541

Cook County
Nina Alizada / Shutterstock

Total Area: 1,635 sq mi or 4,230 km2

Population Density: 3,200/sq mi

With a population of 5,275,541, Cook County is the second most populated county in the United States.

Its most populated city is Chicago, with almost three million people residing. Cook County is well-known for Chicago, its county seat that is popular for tall skyscrapers, Chicago-style hotdogs and pizza, and Millennium Park.

3. Harris County, Texas – 4,731,145

Harris County
lunamarina / Shutterstock

Total Area: 1,778 sq mi or 4,600 km2

Population Density: 2,700/sq mi

Located in the U.S. state of Texas, Harris County has a total of 4,731,145 residents, which accounts for 16% of the total population of Texas.

The county is named after John Richardson Harris, a trader and the founder of the town Harrisburg.

Its seat county is Houston, which is also its largest city.

4. Maricopa County, Arizona – 4,420,568

Maricopa County
AevanStock / Shutterstock

Total Area: 9,224 sq mi or 23,890 km2

Population Density: 480/sq mi

In the U.S. state of Arizona lies Maricopa County, with a population of 4,420,568. More than half of the people in Arizona live in Maricopa County, specifically in Phoenix which is the largest city in the county.

The county was named for the Maricopa people, a Native American tribe known as Piipaash.

5. San Diego County, California – 3,298,634

San Diego City
Sean Pavone / Shutterstock

Total Area: 4,260.9 sq mi or 11,036 km2

Population Density: 837/sq mi

San Diego County is the fifth most populated county with 3,298,634 residents. One of the best-known cities in the county is its county seat San Diego City, also referred to as America’s Finest City.

It is one of the best places for ocean dips at pristine white-sand beaches, seeing wildlife in zoos and parks, and having fun at family-friendly attractions like LEGOLAND California.

6. Orange County, California – 3,186,989

Orange County
Matt Gush / Shutterstock

Total Area: 948 sq mi or 2,460 km2

Population Density: 3,989/sq mi

Orange County, popularly referred to as the OC, is one of the most famous and iconic vacation destinations in the United States.

Many people are drawn to its oceanfront beach towns, beautiful beaches, and the ever-famous Disneyland.

With its perfect weather and safe surroundings, it’s no wonder 3,186,989 residents choose to live here, making it the sixth-most populous county in the country.

7. Miami-Dade County, Florida – 2,701,767

The Sunshine State, Miami-Dade
Susan Santa Maria / Shutterstock

Total Area: 2,431.178 sq mi or 6,296.72 km2

Population Density: 1,422.92/sq mi

Located in The Sunshine State, Miami-Dade County has a population of 2,701,767, ranking it seventh on the list.

The 2,431.178 sq mi county has 34 incorporated municipalities and 38 census-designated places (CDP).

Almost 70% of the population are Hispanic or Latino, while the minority are White, Black or African American, and Asian.

8. Kings County, New York – 2,736,074

 Brooklyn Bridge
Sean Pavone / Shutterstock

Total Area: 97 sq mi or 250 km2

Population Density: 38,634/sq mi

Kings County is often referred to as Brooklyn, a New York City borough. It is the largest county in the U.S. state of New York with a population of 2,736,074.

Tourists come to the county to enjoy its many famous attractions including the Brooklyn Bridge, Coney Island, and Brooklyn Botanic Garden.

9. Dallas County, Texas – 2,613,539

Dallas City
Kevin Ruck / Shutterstock

Total Area: 908.54 sq mi or 2,353.1 km2

Population Density: 2,993.54/sq mi

Dallas County is the second-largest county by population in Texas with a total of 2,613,539 residents.

Its county seat and largest city is Dallas City, with 1,304,379 people residing. At least 40% of the population are Hispanic or Latino, almost 30% are White, and about 22% are Black or African American.

10. Riverside County, California – 2,418,185

inland empire
Tim Gray / Shutterstock

Total Area: 7,303 sq mi or 18,910 km2

Population Density: 336/sq mi

Incorporated in 1893, Riverside County took its name from the City of Riverside and the Santa Ana River.

It has a total population of 2,418,185 with a population density of 336/sq mi or 130/km2. Known for its citrus industry, Riverside city is the county’s county seat and the largest city by population.

11. Queens County, New York – 2,405,464

Queens, NY
Frank Romeo / Shutterstock

Total Area: 178 sq mi or 460 km2

Population Density: 22,124.5/sq mi

The second-largest county in the U.S. state of New York is Queens County, home to 2,405,464 people.

Queens is also a borough of New York City that is situated on the western end of Long Island. The county is famous for art, museums, restaurants, and gardens like the Queens Botanical Garden.

12. Clark County, Nevada – 2,265,461

Clark County
Dominic Gentilcore PhD / Shutterstock

Total Area: 8,061 sq mi or 20,880 km2

Population Density: 280/sq mi

Clark County has 2,265,461 residents, of which 1,771,945 live in Las Vegas, its largest city. The county was founded in 1909 and was named after William Clark Sr. who was an American politician and businessman.

Its economy is fueled by gaming and casino companies, educational institutions, and government organizations.

13. King County, Washington – 2,269,675

Edmund Lowe Photography / Shutterstock

Total Area: 2,307 sq mi or 5,980 km2

Population Density: 980/sq mi

Situated in the U.S. state of Washington, King County is the 13th largest county by population with 2,269,675 residents.

In 2005, it was named for Martin Luther King Jr., a famous African American activist. Most of the people in the county live in its county seat Seattle, specifically in the suburban areas.

14. San Bernardino County, California – 2,181,654

San Bernardino County, California
Andy Konieczny / Shutterstock

Total Area: 20,105 sq mi or 52,070 km2

Population Density: 109/sq mi

In the southern region of California lies San Bernardino County, home to 2,181,654 people. About half of the population is Hispanic or Latino, while Whites account for 25% of the population.

Most of the top attractions of the county are parks and forests including Mojave Narrows Park, Joshua Tree National Park, and San Bernardino National Forest.

15. Tarrant County, Texas – 2,110,640

Tarrant County, Texas
A G Baxter / Shutterstock

Total Area: 902 sq mi or 2,340 km2

Population Density: 2,340/sq mi

Founded in 1850, Tarrant County is the third most populous county in Texas with a population of 2,110,640.

It is bordered by several counties including Dallas County in the east, Denton County in the north, Johnsons County in the south, and Parker County in the west.

The population is composed of approximately 42% White, 30% Hispanic or Latino, 17% African American, 6% Asian, and the rest are other races.

16. Bexar County, Texas – 2,009,324

Bexar County, Texas
f11photo / Shutterstock

Total Area: 1,256 sq mi or 3,250 km2

Population Density: 1,117/sq mi

With a population of 2,009,324, Bexar County is the fourth-largest county in Texas and the 16th-largest by population in the United States.

The county is also home to the most Hispanic residents in Texas, which account for almost 60% of the total population.

San Antonio is the county seat and its largest city, which is also the seventh largest city by population in the country.

17. Broward County, Florida – 1,944,375

Broward County, Florida
Richard Cavalleri / Shutterstock

Total Area: 1,322.817 sq mi or 3,426.08 km2

Population Density: 1,500/sq mi

Nestled in southeastern Florida lies Broward County with 1,944,375 residents. The county was founded in 1915 and was named for Napoleon B. Broward.

There are many sights to explore in the county, from history museums like the Bonnet House Museum & Gardens to nature and wildlife such as Butterfly World.

18. Santa Clara County, California – 1,936,259

Santa Clara
yhelfman / Shutterstock

Total Area: 1,304 sq mi or 3,380 km2

Population Density: 1,500/sq mi

Santa Clara is the sixth largest county in California with a population of 1,936,259, which mostly comprises Whites, Asians, and Hispanics or Latinos.

Its county seat is San Jose, a major city famous for Silicon Valley, public art, and performing arts companies.

The county was incorporated in 1850 and was named for Mission Santa Clara de Asís and St. Clare of Assisi.

19. Wayne County, Michigan – 1,793,561

Wayne County, Michigan
Sean Pavone / Shutterstock

Total Area: 673 sq mi or 1,740 km2

Population Density: 2,974.4/sq mi

Wayne County is Michigan’s largest county by population with 1,793,561 residents. It was created and incorporated in 1796 and is well-known for its county seat Detroit.

The county is bordered by several counties including Washtenaw County to the west, Monroe County to the south, Oakland County to the northwest, and Essex County in Canada to the east.

20. Alameda County, California – 1,682,353

Alameda and Contra Costa Counties
yhelfman / Shutterstock

Total Area: 821 sq mi or 2,130 km2

Population Density: 2,277/sq mi

The 20th largest in the United States and the seventh largest county in California is Alameda County, with a population of 1,682,353.

The county is well known for Oakland – its county seat and major West Coast port. There are eight National Historic Landmarks and several National Historic Places found in the county.

21. Middlesex County, Massachusetts – 1,632,002

Assabet River National Wildlife Refuge
Adam Gladstone / Shutterstock

Total Area: 847 sq mi or 2,190 km2

Population Density: 1,996/sq mi

With 1,632,002 residents, Middlesex County is the largest county in Massachusetts and the 21st largest in the United States.

It stretches a total area of 847 sq mi or 2,190 km2 and shares borders with Essex County, Hillsborough County, Norfolk County, Suffolk County, and Worcester County.

There are several national protected areas in the county such as Assabet River National Wildlife Refuge, Great Meadows National Wildlife Refuge, and Longfellow House–Washington’s Headquarters National Historic Site.

22. Sacramento County, California – 1,585,055

Sacramento County, California
Johnny Habell / Shutterstock

Total Area: 994 sq mi or 2,570 km2

Population Density: 1,600/sq mi

Known as the City of Trees, Sacramento County is one of the most popular counties in the United States with a population of 1,585,055.

It has several historical landmarks including Old Town, Capitol Park, and State Capitol. Its largest city is Sacramento, which is the State Capital with a population of 524,943.

23. New York County, New York – 1,694,251

Empire State Building
Marc Venema / Shutterstock

Total Area: 33.58 sq mi or 87.0 km2

Population Density: 74,780.7/sq mi

New York County is one of the most visited counties in the United States and the world. People flock to its economic and tourist center Manhattan, which is home to world-renowned landmarks such as the Empire State Building, Central Park, and Grand Central Terminal.

1,694,251 people live in the buzzing county, of which half of the population are White and the other half is a mix of African American, Hispanic or Latino, and Asian residents.

24. Philadelphia County, Pennsylvania – 1,603,797

Christian Hinkle / Shutterstock

Total Area: 143 sq mi or 370 km2

Population Density: 11,822/sq mi

Philadelphia County is Pennsylvania’s largest county by population with 1,603,797 residents and is also the second-smallest county by area with a total area of 143 sq mi or 370 km2.

Founded in 1682, the county has the City of Philadelphia or Philly as the county seat and is composed of several boroughs and townships.

Most of the population are White and African American, which is 45% and 43.2% of the population, respectively.

25. Suffolk County, New York – 1,525,920

Long Island
Felix Lipov / Shutterstock

Total Area: 2,373 sq mi or 6,150 km2

Population Density: 1,637.0/sq mi

Located on the eastern tip of Long Island in New York State, Suffolk County has the 25th largest population that is home to 1,525,920 people.

The county stretches a total area of 2,373 sq mi or 6,150 km2, where about 1,637 people live in every square mile.

Suffolk County is known for its suburban neighborhoods, traditional family farms, and historic villages.