Harris County, Texas, added 48,695 residents in a single year, more than any other county in the United States, according to the U.S. Census Bureau’s Vintage 2025 county population estimates, released in March 2026. The estimates cover July 1, 2024, to July 1, 2025, and they show a clear pattern: the counties gaining the most people are concentrated in Texas, Florida, Arizona and the Carolinas, and most of the fastest domestic-migration growth is happening in suburbs and exurbs rather than big cities. This report ranks the top 20 counties by population gain and breaks down where that growth is coming from.
Quick answer: The five U.S. counties that gained the most residents in the latest Census estimates were Harris County, TX (+48,695), Collin County, TX (+42,966), Maricopa County, AZ (+35,411), Montgomery County, TX (+30,011) and Wake County, NC (+27,760). Texas holds 9 of the top 20 spots and Florida holds 4.
Top 20 counties gaining the most residents
The ranking below is based on numeric population change in the Census Bureau’s Vintage 2025 county dataset. Growth rate is calculated from the same file (numeric change divided by the July 2024 estimate). The last two columns show net domestic migration (people moving in from other U.S. counties minus people moving out) and net international migration.
| Rank | County | Population, July 2025 | Gain, 2024–25 | Growth | Net domestic migration | Net international migration |
|---|---|---|---|---|---|---|
| 1 | Harris County, Texas | 5,045,026 | +48,695 | 1.0% | −43,377 | 57,225 |
| 2 | Collin County, Texas | 1,297,179 | +42,966 | 3.4% | 24,102 | 11,749 |
| 3 | Maricopa County, Arizona | 4,689,558 | +35,411 | 0.8% | 941 | 22,132 |
| 4 | Montgomery County, Texas | 781,194 | +30,011 | 4.0% | 22,690 | 3,486 |
| 5 | Wake County, North Carolina | 1,257,235 | +27,760 | 2.3% | 12,790 | 8,602 |
| 6 | King County, Washington | 2,344,939 | +26,980 | 1.2% | −9,079 | 28,428 |
| 7 | Mecklenburg County, North Carolina | 1,233,383 | +26,554 | 2.2% | 4,931 | 13,347 |
| 8 | Fort Bend County, Texas | 975,191 | +24,163 | 2.5% | 10,406 | 8,883 |
| 9 | Williamson County, Texas | 752,827 | +23,814 | 3.3% | 14,764 | 4,618 |
| 10 | Pinal County, Arizona | 539,380 | +23,654 | 4.6% | 21,315 | 1,158 |
| 11 | Polk County, Florida | 874,790 | +23,356 | 2.7% | 18,752 | 3,722 |
| 12 | Denton County, Texas | 1,069,346 | +23,120 | 2.2% | 11,569 | 5,101 |
| 13 | Clark County, Nevada | 2,407,226 | +21,480 | 0.9% | 8,465 | 8,890 |
| 14 | Bexar County, Texas | 2,160,088 | +21,146 | 1.0% | 2,505 | 8,356 |
| 15 | Tarrant County, Texas | 2,248,466 | +18,428 | 0.8% | −6,978 | 12,762 |
| 16 | Pasco County, Florida | 674,516 | +18,326 | 2.8% | 18,078 | 1,851 |
| 17 | Osceola County, Florida | 481,718 | +15,842 | 3.4% | 7,272 | 6,503 |
| 18 | Riverside County, California | 2,544,916 | +15,804 | 0.6% | 7,758 | 810 |
| 19 | Travis County, Texas | 1,389,670 | +14,749 | 1.1% | −6,590 | 11,928 |
| 20 | Marion County, Florida | 442,660 | +14,665 | 3.4% | 15,971 | 1,330 |
Together, these 20 counties added 496,924 residents in one year. About 136,000 of that came from net domestic migration, about 221,000 from net international migration, and about 140,000 from natural increase (births minus deaths), based on summing the Census components for each county.
Texas dominates the list
Nine of the top 20 counties are in Texas: Harris, Collin, Montgomery, Fort Bend, Williamson, Denton, Bexar, Tarrant and Travis. They cluster around the state’s four big metros, Houston, Dallas-Fort Worth, Austin and San Antonio.
The Texas counties split into two groups. Harris (Houston), Tarrant (Fort Worth) and Travis (Austin) grew mainly through immigration and births, while more residents moved out to other U.S. counties than moved in. Their suburban neighbors did the opposite. Collin County, north of Dallas, gained 24,102 people through net domestic migration, the most of any county in the country, and Montgomery County, north of Houston, gained 22,690. Williamson County, north of Austin, added 14,764.
Moving-truck data points in the same direction. The U-Haul Growth Index for 2025 ranked Dallas, Houston and Austin as the top three growth metros in the country based on one-way equipment rentals, and ranked McKinney, the Collin County seat, No. 6 on its list of growth cities.
Two kinds of growth: immigration hubs vs. domestic magnets
A county can gain residents in very different ways, and the Census components make that visible.
Big urban counties grew through immigration
Harris County’s 48,695-person gain came from 57,225 net international migrants and 34,861 more births than deaths, offset by a net domestic loss of 43,377 people. King County, Washington (Seattle) followed the same pattern: +28,428 international migration and −9,079 domestic migration.
The Census Bureau highlighted this dynamic in its release. The 50 counties with 1 million or more people had a combined net domestic migration loss of 637,634. Summing the county file, those same 50 counties gained 637,693 through net international migration, so immigration only just offset the domestic outflow. Census Bureau demographer George M. Hayward noted that the nation’s largest counties “are often international migration hubs.”
Suburbs and exurbs grew through domestic moves
At the other end are counties where almost all growth comes from Americans relocating from elsewhere. Pinal County, Arizona, between Phoenix and Tucson, added 23,654 people, and 21,315 of them came through net domestic migration. Relative to its size, that is about 40 new domestic movers per 1,000 residents, the highest rate among the top 20.
Where Americans are actually moving: top counties by domestic migration
If you strip out immigration and births, the list of counties that are winning over movers from other parts of the U.S. looks different. These are the 10 counties with the largest net domestic migration in the Vintage 2025 estimates:
| Rank | County | Net domestic migration, 2024–25 | Per 1,000 residents |
|---|---|---|---|
| 1 | Collin County, Texas | +24,102 | 18.9 |
| 2 | Montgomery County, Texas | +22,690 | 29.6 |
| 3 | Pinal County, Arizona | +21,315 | 40.4 |
| 4 | Polk County, Florida | +18,752 | 21.7 |
| 5 | Pasco County, Florida | +18,078 | 27.2 |
| 6 | Marion County, Florida | +15,971 | 36.7 |
| 7 | Williamson County, Texas | +14,764 | 19.9 |
| 8 | Horry County, South Carolina | +14,222 | 33.8 |
| 9 | Wake County, North Carolina | +12,790 | 10.3 |
| 10 | St. Johns County, Florida | +12,549 | 36.9 |
Every county on this list is in the Sun Belt, and most are suburban or exurban: Collin and Montgomery outside Dallas and Houston, Pinal outside Phoenix, Pasco outside Tampa, St. Johns outside Jacksonville and Wake around Raleigh. Horry County, South Carolina (Myrtle Beach), and Marion County, Florida (Ocala), round out the list as smaller metros with some of the highest domestic migration rates in the country.
Florida’s growth runs almost entirely on migration
Four Florida counties made the top 20: Polk, Pasco, Osceola and Marion. In two of them, deaths outnumbered births in 2024–25. Pasco County had a natural decrease of 1,405 and Marion County a natural decrease of 2,508, yet both added more than 14,000 residents because of domestic movers. Polk County, between Tampa and Orlando, gained 18,752 people through net domestic migration.
U-Haul’s 2025 city rankings line up closely with those counties. Ocala (Marion County) was the No. 1 growth city in the U-Haul index, Kissimmee (Osceola County) was No. 4, and St. Augustine (St. Johns County) was No. 8. Florida cities took 8 of U-Haul’s top 10 growth city spots.
Not every Florida county is growing, though. The Census Bureau lists Pinellas County (−11,834) and Miami-Dade County (−10,115) among the five counties with the largest numeric losses. Miami-Dade gained 54,204 international migrants but lost 72,254 people to domestic migration.
Growth slowed almost everywhere in 2025
The latest estimates also show a sharp slowdown. According to the Census Bureau’s March 2026 county estimates release, U.S. population growth fell from 1.0% in 2023–24 to 0.5% in 2024–25, and nearly 8 in 10 counties that grew in 2023–24 saw their growth slow or reverse. Net international migration dropped from 8.08 to 3.70 per 1,000 residents nationally, and 9 in 10 counties had lower international migration than a year earlier.
A count of the Census county file shows 1,862 of 3,144 counties, about 59%, gained population over the year. For the counties on this list that depend heavily on international migration, such as Harris, King and Travis, a continued drop in immigration could shrink future gains. The domestic-migration counties, by contrast, are less exposed to that shift.
At the state level, the Census Bureau’s Vintage 2025 state estimates show North Carolina (+84,064), Texas (+67,299) and South Carolina (+66,622) led the nation in net domestic migration, while California (−229,077) and New York (−137,586) had the largest domestic losses. That matches the county picture: the biggest domestic gains are in Texas and the Carolinas.
Counties losing the most residents
The Census Bureau lists the five counties with the largest numeric losses in 2024–25 as Los Angeles County, CA (−53,934), Pinellas County, FL (−11,834), Miami-Dade County, FL (−10,115), Queens County, NY (−8,852) and Orange County, CA (−8,520). Los Angeles County alone lost 105,471 people to net domestic migration, according to the county dataset, the largest domestic outflow of any county.
Moving-industry studies show similar direction at the state level. United Van Lines’ 2025 National Movers Study listed New Jersey, New York and California as its top three outbound states, and South Carolina and North Carolina among its top inbound states.
What this means if you are moving to a high-growth county
Fast-growing counties create a few practical issues for movers. Many of the domestic-migration leaders, such as Collin, Montgomery, Pinal and St. Johns, are adding new subdivisions quickly, and new-construction closings can slip. If your move-in date depends on a builder, ask your mover about storage-in-transit and flexible delivery windows before you sign.
Demand also concentrates in these corridors. When many households are moving into the same metros, especially in summer, booking early matters. For a long-distance move, getting estimates two to three months ahead of a peak-season date gives you more choice of dates and crews.
Finally, compare the whole cost of the move, not just the destination. The Tax Foundation’s 2026 state income tax table shows Texas, Florida and Nevada levy no individual income tax, which is part of the draw for several counties on this list. Property taxes, insurance and HOA fees in fast-growing suburbs can offset some of those savings, so budget for them when you compare destinations.
Methodology
This ranking uses the Census Bureau’s Vintage 2025 county population estimates (the co-est2025-alldata file), which cover the period from July 1, 2024, to July 1, 2025. Counties are ranked by numeric population change (NPOPCHG2025). Components shown are net domestic migration, net international migration and natural change as published by the Census Bureau; they do not always add up exactly to total change because the Bureau also reports a small residual. Growth percentages and domestic migration rates per 1,000 are taken from or calculated with the same file.
Frequently Asked Questions
Which county gained the most residents in the latest Census estimates?
Harris County, Texas, home to Houston, gained 48,695 residents between July 2024 and July 2025, the largest numeric gain of any U.S. county.
Which county gained the most people from domestic migration?
Collin County, Texas, north of Dallas, had the largest net domestic migration, adding 24,102 people who moved in from other U.S. counties, net of those who left.
Which state has the most fast-growing counties?
Texas, with 9 of the top 20 counties by numeric gain. Florida is second with 4 counties.
What was the fastest-growing county by percentage?
Among counties with at least 20,000 residents, the Census Bureau lists Jasper County, South Carolina, as the fastest-growing at 6.0%, followed by Waller County and Kaufman County in Texas at 5.7% each.
Which county lost the most residents?
Los Angeles County, California, lost 53,934 residents in 2024–25, the largest numeric decline of any county, according to the Census Bureau.
Why are big-city counties like Harris growing if people are moving out?
Because international migration and births more than offset domestic outflow. Harris County lost 43,377 people to domestic migration but gained 57,225 through international migration and 34,861 through natural increase.
What time period does this data cover?
The Census Bureau’s Vintage 2025 estimates, released in March 2026, measure population change from July 1, 2024, to July 1, 2025. They are the most recent official county estimates available.
Planning a move to one of these counties
If your next move is headed to Houston’s or Dallas’s suburbs, the Phoenix corridor, central Florida or the Carolinas, you are following the biggest migration flows in the country, and you will be competing with many other households for moving dates. Start with a room-by-room inventory, request at least three written estimates that itemize packing, storage and delivery fees, and book as early as your closing or lease date allows. Interstate Moving and Relocation Group can provide a written, itemized estimate so you can compare it line by line with other quotes.
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