MARCH 23, 2017 — Maricopa County, Ariz., replaced Harris County, Texas, as the county with the nation's highest annual population growth, according to U.S. Census Bureau population estimates released today. Harris County was the largest numeric gainer for eight years in a row. Maricopa County gained 81,360 people between July 1, 2015 and July 1, 2016, or about 222 people per day, while the nation's second-largest population gainer, Harris County, gained 56,587 people, or about 155 people per day on average.

Maricopa County, home to Phoenix, primarily grew through the addition of 43,189 residents from net domestic migration, a measure of how many people move to or from an area versus other parts of the United States. The county also added 25,428 people from natural increase (more births than deaths) and 10,188 people from net international migration.

Harris County, Texas, home to Houston, saw changes in net domestic migration, going from a net gain of more than 17,000 to a net loss of more than 16,000. Despite this, Harris County had the second largest gain in population due to high natural increase (46,412) and net international migration (27,922).

"In the early 2000s, Maricopa County was in the top one or two counties by numeric growth. From 2009-2011, Maricopa County saw much lower net migration than in the years before or after, which caused the county to drop out of the top population-gaining counties," explained Peter Borsella, a demographer in the Census Bureau's population division. "While net international migration has not reached prior levels, net domestic migration and natural increase have continued to rise, making Maricopa County this year's largest numeric gainer."

In addition, Maricopa grew the fastest among the top 10 largest counties at 1.95 percent, an increase from 1.90 percent from the previous year. Harris County remained the third-largest county with 4.6 million people, and Maricopa County remained the fourth-largest county with 4.2 million people. Los Angeles County and Cook County, Ill., remained the largest and second-largest counties, respectively.

The statistics released today provide population estimates and components of change for our nation's 382 metropolitan statistical areas, 551 micropolitan statistical areas, and 3,142 counties, as well as Puerto Rico's metropolitan statistical areas, micropolitan statistical areas and municipios.

Find more highlights from this year's release below and local-level statistics on census.gov.

In the coming months, the Census Bureau will release 2016 population estimates for cities and towns, as well as national, state and county population estimates by age, sex, race and Hispanic origin.