International migration drove the majority of growth for Maricopa County last year.
The U.S. Census Bureau says according to the latest estimates that without a net increase in migration, the falling birth rate and exodus of domestic residents would have led the biggest counties to see flat or falling numbers.
Maricopa County was the third-fastest growing, following Harris County in Texas at Number 1 and Miami-Dade in Florida at Number 2.
Two-thirds of the counties in the country grew last year, the largest counties, those over 100,000 people, grew faster than smaller ones.
That reversed a trend seen in the first few years of the COVID-19 pandemic.
Immigration in 2024 drove the overall U.S. population growth to its fastest rate in 23 years as the nation surpassed 340 million residents. The Census Bureau changed how it counted immigrants last year by including more people who were admitted to the U.S. for humanitarian, and often temporary, reasons.
“A substantial excess of births over deaths has long been the primary driver of U.S. population growth, but as this surplus dwindled in the last four years immigration provided the bulk of the nation’s population increase,” Kenneth Johnson, a senior demographer at the University of New Hampshire, said in an email.
