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The most populous counties in the US, 2010 to 2025

Los Angeles County is still the largest US county at 9.69 million in 2025, but Harris County, Texas, has added 937,000 people since 2010.

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What the data shows

  • In 2025, Los Angeles County, California ranks #1 with 9.70M, ahead of Cook County, Illinois (5.20M) and Harris County, Texas (5.05M).
  • Los Angeles County, California holds #1 for the whole period, 2010 to 2025.

About this chart

Los Angeles County has the most residents of any US county, with 9,694,934 in 2025, but it has shrunk from 9,821,647 in 2010 and a peak of about 10.1 million in 2016. Cook County, Illinois, is second at 5,194,625 and essentially flat over the period. The growth is in the Sun Belt: Harris County, Texas, reached 5,045,026 and Maricopa County, Arizona, 4,689,558.

Harris County added about 937,000 people since 2010 and Maricopa about 864,000. Further down, Dallas County (2,661,397) edged past Kings County, New York (2,653,963), and Riverside County, California (2,544,916) passed Queens County (2,358,182). Figures are Census Bureau July 1 estimates, using Vintage 2020 through 2019 and Vintage 2025 from 2020, which is why several counties jump in 2020.

The data

Source: U.S. Census Bureau, county population estimates (Vintage 2020 for 2010–2019, Vintage 2025 for 2020–2025), July 1, millions. Retrieved November 4, 2026.

Most populous US counties, Residents in millions, 2010 to 2025, 2010–2025
DateLos Angeles County, CaliforniaCook County, IllinoisHarris County, TexasMaricopa County, ArizonaSan Diego County, CaliforniaOrange County, CaliforniaMiami-Dade County, FloridaDallas County, TexasKings County, New YorkRiverside County, CaliforniaQueens County, New York
20109.82M5.20M4.11M3.83M3.10M3.02M2.51M2.37M2.51M2.20M2.24M
20119.87M5.22M4.18M3.88M3.14M3.05M2.55M2.41M2.54M2.23M2.26M
20129.93M5.24M4.26M3.95M3.18M3.08M2.58M2.46M2.57M2.26M2.27M
20139.99M5.25M4.35M4.02M3.21M3.11M2.61M2.49M2.59M2.29M2.29M
201410.03M5.25M4.46M4.10M3.25M3.13M2.63M2.52M2.60M2.32M2.30M
201510.08M5.24M4.56M4.17M3.28M3.15M2.66M2.56M2.61M2.35M2.31M
201610.10M5.22M4.62M4.26M3.31M3.16M2.69M2.59M2.61M2.38M2.31M
201710.09M5.20M4.66M4.33M3.32M3.17M2.71M2.62M2.59M2.41M2.30M
201810.06M5.17M4.68M4.41M3.33M3.18M2.71M2.63M2.58M2.44M2.28M
201910.01M5.15M4.71M4.49M3.33M3.17M2.71M2.64M2.56M2.47M2.25M
202010.00M5.26M4.73M4.45M3.30M3.19M2.70M2.61M2.72M2.42M2.39M
20219.81M5.19M4.74M4.50M3.27M3.16M2.67M2.59M2.64M2.46M2.33M
20229.75M5.13M4.81M4.56M3.28M3.16M2.73M2.61M2.60M2.48M2.29M
20239.73M5.14M4.90M4.60M3.28M3.15M2.79M2.64M2.61M2.50M2.32M
20249.75M5.19M5.00M4.65M3.29M3.16M2.81M2.66M2.66M2.53M2.37M
20259.70M5.20M5.05M4.69M3.28M3.15M2.80M2.66M2.65M2.55M2.36M

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Frequently asked questions

What is the most populous county in the US?

In 2025, Los Angeles County, California ranks #1 with 9.70M, followed by Cook County, Illinois (5.20M) and Harris County, Texas (5.05M). Source: U.S. Census Bureau, county population estimates (Vintage 2020 for 2010–2019, Vintage 2025 for 2020–2025), July 1, millions.

What is the most populous county in the US?

Los Angeles County, California, with about 9.69 million residents (9,694,934) in July 2025, according to Census Bureau estimates. Cook County, Illinois, is second at 5.19 million.

Which large counties are growing fastest?

Harris County, Texas, grew from 4.11 million in 2010 to 5.05 million in 2025, and Maricopa County, Arizona, grew from 3.83 million to 4.69 million. Both are up more than 20 percent.

Is Los Angeles County losing population?

Yes, slowly. It had 9.82 million residents in 2010, peaked near 10.1 million in 2016, and stood at 9.69 million in 2025.

Where does this data come from?

U.S. Census Bureau, county population estimates (Vintage 2020 for 2010–2019, Vintage 2025 for 2020–2025), July 1, millions. Retrieved November 4, 2026. You can download the full table as a CSV from this page.

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