9 Most Populated Counties in the US

The US’s most populous counties are typically found in the vicinity of large cities. One city can include millions of people, which can skew statistics by holding a substantial portion of the county’s total population.

However, this does not imply that the most populous counties remain unchanged. Populations have changed over time. Every year, the number of people relocating to the west and south increases. This indicates that the population of the northeastern states and the counties that make up them has been gradually declining.

Furthermore, people can now reside in tiny US communities rather than big cities thanks to remote work. The two most populous counties in the country, however, have maintained their rankings in spite of everything.

Look through the list below to find out which are the two most populated and stable counties, along with the other counties that are lagging behind.

1. Los Angeles County, California

The population of Los Angeles County, California, is predicted to be 10 million. With a total length of 4,057 miles, the nation is both one of the largest and most populous in the United States. This indicates that the county’s population density is about 2,465 persons per square mile.

Founded in 1850 along with the state, the county seat is located in Los Angeles. The county contains 87 smaller towns and communities in addition to this principal city. Los Angeles County is home to about 25% of California’s population.

2. Cook County, Illinois

Cook County, which located in Illinois, is home to 5.27 million people overall. With a total area of 945 miles, this county has roughly 5,583 people per square mile.

The only large city in the county is the main factor contributing to its high population. Approximately half of the county’s population resides in Chicago, the county seat.

3. Harris County, Texas

Texas’s southeast region is home to Harris County. There are 4.7 million individuals dispersed over 1,703 miles. It is comparable to Los Angeles County, which has 2,760 inhabitants per square mile.

Houston serves as the county seat. It’s interesting to note that more than 83% of Harris County’s population was reared there. It was first known as Harrisburg County in 1836. But in honor of John R. Harris, the name was changed to Harris County in 1839.

4. Maricopa County, Arizona

There are 4.4 million people living in Maricopa County, which features Phoenix as its county seat. Even while this seems like a lot, it covers a significant amount of ground—more than 9,200 miles. This indicates that the population density per square mile is only about 480. Of the 4.4 million, 1.63 million call Phoenix home.

This county is home to more than half of Arizona’s population and is expected to grow at the fastest rate in the country by 2022. Over 56,000 people relocated to the area in 2021–2022. Not only is it the most populous county in Arizona, but it’s also one of the oldest and has a rich historical background.

5. San Diego County, California

San Diego County, California is the second Californian entry on this list. The southernmost point of the state is where this county is situated. San Diego County, with 3.3 million residents, comes in sixth. The population density is barely 779 persons per square mile, despite the land area being 4,207 miles.

The fact that San Diego County is home to 18 tribal reservations—more than any other county in the state—is one of its distinctive features. The region contains 70 miles of coastline as well. This portion of the state was a part of Mexico until 1848.

6. Orange County, California

Near the top of the list is Orange County. With 3.19 million residents, it ranks sixth among the most populous counties in the United States. In spite of this, given that it only occupies 790 miles, it is a densely inhabited region. In other words, 4,031 persons live for every square mile.

Santa Ana serves as the county seat. The dense population makes sense—it’s one of Los Angeles’ metropolitan areas. In actuality, it ranks second in California in terms of population density, only behind San Francisco County. Anaheim, Santa Ana, and Irvine are the three cities that house the majority of the population.

7. Miami-Dade County, Florida

With 2.70 million residents, Miami-Dade County, Florida, ranks eighth in terms of population. Given the size of the county (1,898 miles), the population density is around 1,424 persons per square mile.

Even though Miami, a large metropolis, is a part of Miami-Dade County, a large portion of the region is composed of agricultural land and natural parks. Despite the high population density in Miami and certain other regions of the county, this contributes to the lower population level. To the west lies the vast Everglades National Park, and to the east are the Aquatic Preserves and Biscayne National Park.

8. Dallas County, Texas

Dallas, which is a city in Dallas County, Texas, is home to 1.22 million of the 2.6 million residents in the county, or about half. Because of its tiny size, the county has a population density of roughly 3,000 persons per square mile. Dallas County extends little in all directions, but it largely encloses the metropolis.

1846 saw its founding. Although not much is known about its origins, it is believed that George Mifflin Dallas, the 11th Vice President of the United States, inspired the city’s name, Dallas.

9. Kings County, New York

Located in an area less than 71 square miles, Kings County, New York, is home to slightly under 2.6 million people, making it the most densely inhabited county on our list. As a result, there are approximately 36,579 persons per square mile.

Since the county only includes Brooklyn, the population density provides valuable insight into the densely populated nature of large cities like Brooklyn. In actuality, however, Brooklyn is not a separate city but rather a borough of New York.

Overview of the Most Populated Counties in the US

List Number County Name State Population County Seat
1 Los Angeles County California 10,014,009 Los Angeles
2 Cook County Illinois 5,275,541 Chicago
3 Harris County Texas 4,731,145 Houston
4 Maricopa County Arizona 4,420,568 Phoenix
5 San Diego County California 3,298,634 San Diego
6 Orange County California 3,186,989 Santa Ana
7 Miami-Dade County Florida 2,701,767 Miami
8 Dallas County Texas 2,613,539 Dallas
9 Kings County New York 2,590,516 Brooklyn