Most Populated Counties in US 2026 | Demographics & Facts

The most populated county in the US in 2026 is Los Angeles County, California, with 9,694,934 residents as of the Census Bureau’s July 1, 2025 estimate, followed by Cook County, Illinois (5,194,625) and Harris County, Texas (5,045,026). Harris County posted the largest numeric gain of any US county in 2025, adding 48,695 residents, while Los Angeles County recorded the steepest decline of any county, losing 53,934.

Most Populated Counties in the US

The most populated counties in the US anchor the country’s economy and culture even as their growth patterns shift dramatically year to year. Los Angeles County alone holds nearly 9.7 million people, more than 21 individual US states, and the ten largest counties combined house roughly 44 million Americans inside a small fraction of the nation’s total land area. These places are not static rankings frozen in time; several of the counties long assumed to be permanently at the top are now shrinking, while once-modest suburban counties in Texas, Georgia, and North Carolina post double-digit growth rates that would have seemed implausible a decade ago.

The 2026 county population picture, built on the Census Bureau’s Vintage 2025 estimates released in March, shows a nation where growth itself has slowed sharply. National population grew by just 0.5% between 2024 and 2025, roughly half the prior year’s pace, and nearly eight in ten counties that were growing in 2024 saw that growth slow or reverse in 2025. This report walks through exactly which counties hold the largest populations, which ones are gaining and losing residents fastest, and what’s driving the shift beneath the surface.

Interesting Facts About US County Populations in 2026

The national growth rate cooling to 0.5% is not evenly distributed. Counties with 1 million or more residents collectively lost 637,634 people to domestic migration in 2025, even as births continued to outpace deaths inside most of them, meaning international migration was doing nearly all the work keeping their populations from shrinking outright. When that international inflow slowed — nine out of ten US counties saw lower international migration in 2025 than the year before — the largest counties felt it first and hardest.

Mid-sized counties told the opposite story. Places with 50,000 to 999,999 residents gained a combined 533,766 people through domestic migration alone, confirming a pattern demographers have tracked for several years now: Americans are leaving the biggest metro cores for suburban and mid-sized counties, particularly across the Sun Belt. That redistribution explains why a county like Texas’s Collin County can post 21.9% growth since 2020 while Los Angeles County shrinks by more than 300,000 residents over the same stretch.

Top 10 Most Populated Counties in the US 2026

TOP US COUNTIES BY POPULATION — JULY 2025
Los Angeles, CA   ████████████████████████████████████  9.69M
Cook, IL          ████████████████████                 5.19M
Harris, TX        ███████████████████                 5.05M
Maricopa, AZ      ██████████████████                 4.69M
San Diego, CA     █████████████                    3.28M
Orange, CA        █████████████                    3.15M
Miami-Dade, FL    ███████████                    2.80M
Dallas, TX        ██████████                     2.66M
Kings, NY         ██████████                     2.65M
Riverside, CA     ██████████                    2.54M

Source: U.S. Census Bureau, Vintage 2025 Population Estimates.

Los Angeles County has held the number-one spot for decades and remains far ahead of second-place Cook County by roughly 4.5 million people, but its trajectory has reversed. The county has lost population in five straight years, falling from just over 10 million at the 2020 Census to 9,694,934 in the 2025 estimate — a drop of more than 319,000 residents, or 3.2%. Cook County, home to Chicago, follows a similar downward pattern, while Harris County, Texas has taken the opposite path, growing by 313,881 people since 2020 and closing in on Cook County’s second-place position.

Four of the top ten counties are in California, but only Riverside County among them is actually growing. Texas holds two spots in the top ten — Harris and Dallas — and both are expanding, part of a broader pattern where every major Texas county appears somewhere on the nation’s fastest-growing lists. Kings County, coterminous with Brooklyn, is the most geographically compact county on this list by a wide margin, packing 2.65 million people into just 70.82 square miles, a detail that becomes central once population density enters the picture.

Fastest-Growing Counties in the US 2026

LARGEST NUMERIC POPULATION GAINS — 2024 TO 2025
Harris, TX        ████████████████████████████████████  +48,695
Collin, TX        ██████████████████████████████████    +42,966
Maricopa, AZ      ██████████████████████████████       +35,411
Montgomery, TX    ██████████████████████████          +30,011
Wake, NC          ████████████████████████            +27,760
King, WA          ███████████████████████             +26,980

Source: U.S. Census Bureau, Vintage 2025 Population Estimates.

Texas counties occupy five of the ten fastest-growing spots by raw numeric gain, and all five sit inside just two metro areas: Houston and Dallas-Fort Worth. Harris County’s +48,695 residents make it the single largest gainer in the country for the second consecutive vintage, driven mostly by Houston’s continued role as an international migration hub combined with steady natural increase. Collin County, a Dallas-Fort Worth suburb anchored by McKinney, grew 21.9% since the 2020 Census alone, the fastest rate of any county in the current top ten by population.

Outside Texas, the pattern points firmly toward the Sun Belt and the Pacific Northwest. Wake County (Raleigh) and Mecklenburg County (Charlotte) both cracked the top ten on the strength of North Carolina’s ongoing tech and finance sector expansion, while King County, Washington reversed years of pandemic-era stagnation to post its strongest growth since 2019. Arizona placed two counties on this list — Maricopa and Pinal — confirming Phoenix’s outer suburbs remain among the most reliable growth engines in the country even as growth nationally has cooled.

Counties With the Steepest Population Decline in the US 2026

LARGEST NUMERIC POPULATION LOSSES — 2024 TO 2025
Los Angeles, CA    ████████████████████████████████████  -53,934
Pinellas, FL       ████████                              -11,834
Miami-Dade, FL     ███████                               -10,115
Queens, NY         █████                                 -8,852
Orange, CA         █████                                 -8,520
San Diego, CA      ███                                   -5,294

Source: U.S. Census Bureau, Vintage 2025 Population Estimates.

Los Angeles County’s -53,934 loss in a single year dwarfs every other county in the country by a factor of nearly five, and it marks the fifth consecutive year of decline for a county that once seemed destined to reach 11 million residents. The two Florida counties on this list, Pinellas and Miami-Dade, represent a genuinely new trend rather than a continuation of an old one: both had been growing steadily for years before international migration slowdowns exposed underlying domestic outflows that were previously masked.

New York and California together account for six of the ten steepest declines, reinforcing that population loss in America’s largest counties is not a single-state story but a structural pattern affecting the country’s biggest, densest urban cores simultaneously. Dallas County’s appearance at number nine is notable precisely because it sits inside one of the fastest-growing metro areas in the country — proof that even booming regions can see their core county lose residents to surrounding suburbs like Collin and Denton at the same time the metro area as a whole expands.

Population Density of the Largest US Counties in 2026

POPULATION DENSITY — PEOPLE PER SQUARE MILE
Manhattan (NY County)     ████████████████████████████████████   72,924
Kings, NY (Brooklyn)      █████████████████████████████████████  37,477
Cook, IL                  █████                                  5,496
Orange, CA                ████                                   3,984
Dallas, TX                ███                                    3,055
Harris, TX                ███                                    2,962
Los Angeles, CA           ██                                     2,389
Miami-Dade, FL            █                                      1,477

Source: U.S. Census Bureau land area figures paired with Vintage 2025 population estimates.

Raw population totals tell only part of the story, and density flips the rankings almost completely. Manhattan packs 72,924 people into each square mile, more than thirty times denser than Los Angeles County despite having a fraction of its total population, because Los Angeles County’s 4,057.88 square miles include vast stretches of desert, mountains, and low-density suburbs alongside its urban core. Brooklyn’s Kings County follows a similar logic at 37,477 people per square mile, confirming that New York City’s outer boroughs remain the densest large populations anywhere in the country.

Sun Belt counties sit at the opposite end of this spectrum almost without exception. Maricopa County, Arizona’s fourth-most-populous county overall, spreads its 4.69 million residents across 9,200 square miles, yielding a density under 510 people per square mile — roughly one-seventh of Cook County’s figure despite having a comparable total population. That gap explains why Sun Belt growth looks so different on the ground than Northeastern growth: adding a million people to Maricopa County means building outward across open desert, while adding the same number to Kings County would be physically close to impossible within existing boundaries.

Migration Patterns Driving County Population Change in 2026

NET DOMESTIC MIGRATION BY COUNTY SIZE — 2025
1 Million+ Counties        ████████████████████████████████  -637,634
Large (50K-999K)           ██████████████████████████████    +533,766
Medium (15K-49,999)        ██████                             +95,095

Source: U.S. Census Bureau, Vintage 2025 Population Estimates, Components of Population Change.

The migration data explains almost everything else in this report. America’s 50 counties with a million or more residents collectively lost 637,634 people to domestic migration in a single year, meaning far more residents moved out to other parts of the country than moved in from elsewhere in the US. Those same counties kept growing, or at least kept from shrinking faster, largely because international migration flowed disproportionately into them — until that inflow itself dropped sharply nationwide, with nine in ten US counties recording lower international migration in 2025 than in 2024. Similar demographic redistribution shows up clearly in the country’s broader net migration figures, which track the same slowdown at the national level.

Mid-sized and large-but-not-massive counties absorbed almost exactly what the biggest counties lost. Counties in the 50,000 to 999,999 range gained 533,766 domestic migrants, and even medium counties in the 15,000 to 49,999 range posted a positive 95,095. That’s not a coincidence — it’s the same households leaving Los Angeles, Cook, and Miami-Dade counties for exactly these size tiers, a pattern consistent with the broader rural and urban migration trends reshaping where Americans choose to live after the remote-work era changed what proximity to a major employer actually requires.

Fastest-Growing Metro Areas in the US 2026

LARGEST METRO AREA GAINS — 2024 TO 2025
Houston, TX             ████████████████████████████████████  +126,720
Dallas-Fort Worth, TX   ███████████████████████████████████   +123,557
Atlanta, GA             ███████████████████                    +61,953
Phoenix, AZ             ██████████████████                     +59,065
Charlotte, NC-SC        █████████████████                      +54,122

Source: U.S. Census Bureau, Vintage 2025 Population Estimates, Metropolitan Statistical Areas.

Texas metro areas claimed the top two spots outright, with Houston adding 126,720 residents and Dallas-Fort Worth close behind at 123,557, together accounting for a meaningful share of all US metro growth in a year when total metro-area expansion slowed to 0.6% from 1.1% the previous year. Three of the eight fastest-growing metro areas by raw numbers sit inside Texas, echoing the county-level data almost exactly, since Harris, Collin, Montgomery, Fort Bend, and Williamson counties all rank among the nation’s fastest-growing counties individually.

Atlanta and Charlotte represent the Southeast’s continued pull, both benefiting from corporate relocations and lower costs of living relative to coastal metros. Washington-Arlington-Alexandria’s appearance at number seven is a genuine surprise given the slower federal employment growth of recent years, though its 50,206 gain still trails well behind the Sun Belt leaders. Seattle-Tacoma-Bellevue rounds out the list, confirming the Pacific Northwest has returned to steady growth after several years of pandemic-driven stagnation tied to remote work and cost-of-living pressures pushing residents toward smaller Washington counties.

Frequently Asked Questions About the Most Populated Counties in the US 2026

What is the most populated county in the US in 2026?

Los Angeles County, California is the most populated county in the US, with 9,694,934 residents as of the July 2025 Census Bureau estimate.

Which US county grew the most in 2025?

Harris County, Texas grew the most in raw numbers, adding 48,695 residents between July 2024 and July 2025.

Which US county lost the most population in 2025?

Los Angeles County, California lost the most population of any US county, declining by 53,934 residents in a single year.

What is the most densely populated county in the US?

New York County (Manhattan) is the most densely populated large county, with roughly 72,924 people per square mile.

How many counties are there in the United States?

The United States has 3,144 counties and county equivalents, including parishes in Louisiana and boroughs in Alaska.

Is Los Angeles County still the largest county in the US?

Yes. Despite five consecutive years of population decline, Los Angeles County remains the largest US county by a margin of roughly 4.5 million people over second-place Cook County.

Why are large US counties losing population to smaller ones?

Large counties are losing residents to domestic migration as households relocate to mid-sized suburban counties, while reduced international migration has removed the offsetting inflow that previously masked those losses.

What US state has the most people living in a single county?

California holds the single most populous county in the country, Los Angeles County, though Texas places the most counties overall among the nation’s fastest-growing list.

Disclaimer: This research report is compiled from publicly available sources. While reasonable efforts have been made to ensure accuracy, no representation or warranty, express or implied, is given as to the completeness or reliability of the information. We accept no liability for any errors, omissions, losses, or damages of any kind arising from the use of this report.

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