The 10 Most Populous U.S. Counties

The U.S. is not only divided into 50 states but also more than 3,100 counties. These administrative regions manage local law enforcement, public health, judicial courts, and other important affairs. Curiously, though, not every state calls them counties — in Alaska, these subdivisions are called boroughs, while in Louisiana they are referred to as parishes. Whatever they’re called, counties comes in all different sizes, from some with fewer than 100 residents to ones millions of people call home. These are the 10 biggest U.S. counties in terms of population. 

10. Riverside County – California (2.51 Million People)

Riverside County begins east of Los Angeles and stretches across Southern California all the way to the Arizona border. The county isn’t just home to over 2.5 million people — it’s also a region of diverse landscapes, ranging from the deserts of the Coachella Valley to the sprawling Temecula Valley wine region. The county seat, Riverside, is famous for its abundance of lemon trees — a citric heritage that is celebrated at California Citrus State Historic Park. Riverside County is also known for Palm Springs, a resort city in the Sonoran Desert, and the beautiful scenery of Joshua Tree National Park. Once a stomping ground for mammoths and saber-toothed cats in prehistoric times, it’s now popular for hiking, stargazing, and rock climbing.

9. Kings County – New York (2.53 Million)

Kings County comprises the entire borough of Brooklyn, the most populated of New York City’s five boroughs. Occupying the western portion of Long Island, the county originated as a Dutch settlement called Breuckelen. Immigration has long played a role in the cultural identity of Kings County. This is evident on almost every street corner, in vibrant neighborhoods such as Bushwick, Dumbo, and Williamsburg. Notable sights here include the iconic Brooklyn Bridge and exquisite art collections at Brooklyn Museum. There’s plenty on offer for outdoor enthusiasts, too — including Dyker Beach Park, Prospect Park, and Shirley Chisholm State Park.

8. Dallas County – Texas (2.61 Million)

Mapped out in a perfect square in northern Texas, Dallas County is the state’s second-most populous county. At its geographic center is the county seat, Dallas, with a collection of surrounding suburbs that form the Dallas-Fort Worth metropolitan area. Texas’ third-largest city welcomes visitors with a thriving arts, food, and sports scene — look no further than the 20-block Dallas Arts District, the bistros and clubs of Uptown, and American Airlines Center for NBA and NHL games. Those seeking encounters with nature can find it at Cedar Hill State Park and around the shores of Lake Ray Hubbard, among many other places.

7. Miami-Dade County – Florida (2.70 Million)

The most populous county in Florida, Miami-Dade County stretches across the state’s southeastern corner, from the Atlantic coast across vast swathes of wetlands. Situated on land inhabited by nomadic tribes some 10,000 years ago, the county was created in 1836 and named after soldier Francis L. Dade. From the 1960s onward, large numbers of Hispanic communities moved to the county’s coastal towns, and that history is still reflected in vibrant areas such as Miami’s Little Havana neighborhood. Beach-going and nightlife are also part of the county fabric, as are breathtaking natural wonders such as Biscayne National Park and the gator-filled wetlands of Everglades National Park. 

6. Orange County – California (3.12 Million)

Immortalized in the television series The O.C., Orange County is located south of Los Angeles, stretching from the Pacific Ocean to the Santa Ana Mountains in the east. Its largest city, Anaheim, is home to Disneyland, the first Disney theme park, and nearby Buena Park is home to the Knott’s Berry Farm theme park. Orange County’s blissed-out California surf lifestyle can be experienced at spots such as Huntington Beach, Newport Beach, and Laguna Beach. Inland, the Santa Ana Mountains offer hiking trails that weave around both Limestone Canyon Nature Preserve and Ronald W. Caspers Wilderness Park.

5. San Diego County – California (3.26 Million)

Located immediately south of Orange County and stretching all the way to the U.S.-Mexico border is San Diego County. Once part of Alta California under the Viceroyalty of New Spain, and later part of Mexico, it became one of California’s original counties in 1850. Prior to this, archaeological studies have recorded 10,000 years of habitation here. Today, much like the O.C., San Diego County is famous for its beach culture, especially the towns of Encinitas and Oceanside. San Diego, the county seat and largest city, combines laid-back coastal living with watersports, maritime history, and vibrant food and nightlife scenes. Anza-Borrego Desert State Park and Cleveland National Forest are two of the county’s most popular inland nature areas.

4. Maricopa County – Arizona (4.61 Million)

Defined by desert landscapes and nearly 300 days of sunshine per year, Maricopa County is home to more than half of Arizona’s population. Not only is it the largest county in Arizona, but it also covers more land area than four U.S. states: New Jersey, Connecticut, Delaware, and Rhode Island. The county is named after a Native American tribe that lives in the Salt River Pima-Maricopa Indian Community. With over 120,000 acres of green spaces, the county also has one of the largest park systems in the country. Highlights include South Mountain Park and Preserve at the edge of Phoenix and Lake Pleasant Regional Park, popular for boating and fishing.

3. Harris County – Texas (4.88 Million)

Bordering Trinity Bay and encompassing a large portion of the Greater Houston metropolitan area, Harris County is the most populous county in Texas. Houston — a city built on its aerospace, energy, and health care industries — is the county seat. It’s also a big draw for sports fans, who can see MLB’s Houston Astros compete at Minute Maid Park or the Houston Texans play in the NFL at NRG Stadium. NASA Johnson Space Center, the site of mission control and astronaut training facilities, is another county landmark where curious minds can delve into space exploration past and present. 

2. Cook County – Illinois (5.06 Million)

With Chicago at its heart, Cook County hugs the southwestern shoreline of Lake Michigan. The nation’s second-most populous county, it was created in 1831 with the lakeside settlement of Fort Dearborn (which was later incorporated into Chicago) as its original county seat. Once notorious for its criminal underground, Cook County has housed numerous notorious lawbreakers — including Al Capone and Frank Nitti — at its eponymous jail. Today, the county is more famous for museums like the Art Institute of Chicago, shopping along the Magnificent Mile, and sprawling Grant Park. In the summer months, county residents flock to the golden sands of Kathy Osterman Beach and other scenic spots on Lake Michigan.

1. Los Angeles County – California (9.60 Million)

Home to around 27% of Californians, Los Angeles County is the most populous county in the United States — and it isn’t even close. L.A. County was established in 1850 at the time of California’s statehood and is one of the state’s original 27 counties. Wedged between the beach and mountains, it features an enchanting mix of urban and natural landscapes. The northern section is dominated by the San Gabriel Mountains and recreation areas such as Angeles National Forest. Farther south, you’ll find the hub of the film industry in Hollywood, Sunset Boulevard’s legendary music venues, and thriving beach communities such as Santa Monica, Venice Beach, and Long Beach.