400 counties
According to the most recent United States Census, Los Angeles County in California is the largest county in the nation, with a total population of 9,550,505 – a decrease of 4.4% since 2020. Chicago's Cook County follows and, although very large in its own right, is about half the size of Los Angeles County with 5,038,084 residents. Harris County in Texas, Maricopa County in Arizona, and San Diego County in California make up the rest of the top five – all have populations in excess of three million.
| County | State | 2025 Pop. ↓ |
|---|---|---|
| Los Angeles County | California | 9,550,505 |
| Cook County | Illinois | 5,038,084 |
| Harris County | Texas | 4,942,701 |
| Maricopa County | Arizona | 4,645,947 |
| San Diego County | California | 3,255,567 |
Recent statistics show remarkable population growth in several Texas counties since 2020. Kaufman County leads with a dramatic 44% increase, followed by Comal County at 29.7%. Parker County and Ellis County also saw significant growth at 26.1% and 25.5% respectively. The only non-Texas county in the top five is St. Johns County, which has experienced a 24.9% population increase since 2020.
| County | State | Change (2020) ↓ |
|---|---|---|
| Kaufman County | Texas | 43.98% |
| Comal County | Texas | 29.71% |
| Parker County | Texas | 26.11% |
| Ellis County | Texas | 25.49% |
| St. Johns County | Florida | 24.93% |
Recent statistics show significant population declines in several urban areas since 2020. Bronx County experienced the steepest drop at 10.6%, followed by St. Louis city at 9.2%. Orleans Parish saw an 8% decrease, while two more New York City boroughs rounded out the top five: Queens County and Kings County declined by 7.9% and 7.9% respectively.
| County | State | Change (2020) ↑ |
|---|---|---|
| Bronx County | New York | -10.63% |
| St. Louis city | Missouri | -9.19% |
| Orleans Parish | Louisiana | -8% |
| Queens County | New York | -7.93% |
| Kings County | New York | -7.87% |