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.

These notable high-population counties continued to see population loss:

• Cook County, Ill. (Chicago): -21,324.
• Wayne County, Mich. (Detroit): -7,696.
• Baltimore city, Md.: -6,738.

Baltimore city saw an increase in population loss this year primarily due to a doubling of its net domestic out-migration.

Three of the 20 fastest-growing metro areas between 2015 and 2016 were located either partially or completely in Utah (St. George, Utah; Provo-Orem, Utah; and Logan, Utah-Idaho).

• Provo-Orem, Utah, and Logan, Utah-Idaho, saw natural increase as a larger component of growth than either net international migration or net domestic migration, while St. George, Utah, saw net domestic migration as a larger component of growth than either net international migration or natural increase. 
  
• Also, San Juan County, Utah, was the fastest-growing county in the United States among counties with populations of 10,000 or more in 2015. It grew by 7.6 percent.
  

North Dakota counties no longer top the list of fastest-growing counties by percentage change.

• McKenzie County fell from second-fastest growing by percentage change to 2,858th.
• Williams County fell from third to 3,105th.
• Mountrail County fell from sixth to 2,375th.
• Stark County fell from eighth to 3,103rd.

All of these counties lost population due to people moving away to other parts of the United States (negative net domestic migration). Formerly fast-growing North Dakota counties have been replaced in the top 10 by counties in Iowa, Oregon and Washington. Other top 10 counties once again are in Utah, Texas and Florida.

• Eight of the 10 counties with the most natural decrease (more deaths than births) were in Florida. Four of the top 10 counties with the most natural increase were in California, and 3 of the 10 were in Texas.
• St. Louis County, Mo., dropped below 1 million for the first time since 2011, largely due to a rise in net domestic out-migration.
• Three counties reached a population milestone of 100,000 or higher: Fairbanks North Star Borough, Alaska; Highlands County, Fla., and Carver County, Minn.
• Pasco County, Fla., reached a population of 500,000, and Tarrant County, Texas, reached 2 million.

• The nation's 382 metro areas contained approximately 277.1 million people in 2016, representing approximately 86 percent of the nation's population. This was an increase of approximately 2.3 million people from 2015.
• For the fourth year in a row, The Villages, Fla., a metro area west of the Orlando-Kissimmee-Sanford, Fla., metro area, was the nation's fastest-growing metro area, with a 4.3 percent population increase between 2015 and 2016.
• The Dallas-Fort Worth-Arlington, Texas, and Houston-The Woodlands-Sugar Land, Texas, metro areas were the two largest numeric-gaining metro areas between 2015 and 2016, increasing by more than 100,000 each.
• Four metro areas were among both the 25 fastest growing and the 25 largest numeric gaining between 2015 and 2016: Austin-Round Rock, Texas; Raleigh, N.C.; Orlando-Kissimmee-Sanford, Fla.; and Las Vegas-Henderson-Paradise, Nev. For all four areas, net domestic migration was a larger component of change than either net international migration or natural increase
• Among the 10 largest metro areas, the Chicago-Naperville-Elgin, Ill.-Ind.-Wis., metro area was the only metro area that did not grow in population between 2015 and 2016.

• The nation’s 551 micro areas contained approximately 27.7 million people in 2016, representing approximately nine percent of the nation’s population. This is an increase of approximately 16,000 people from 2015.
• Micro areas in the West grew the most.
  • Heber, Utah, was the fastest-growing micro area, with an increase of 4.7 percent between 2015 and 2016. The five fastest-growing micro areas were in the West: Heber, Utah; Prineville, Ore.; Ellensburg, Wash.; Bozeman, Mont.; and Cedar City, Utah. Among these five areas, net domestic migration was a larger component of change than either net international migration or natural increase.
  • Bozeman, Mont., had the largest numeric gain among micro areas between 2015 and 2016, increasing by approximately 3,800 people. Four of the five largest numeric-gaining micro areas between 2015 and 2016 were in the West: Bozeman, Mont.; Hilo, Hawaii; Kalispell, Mont.; and Oak Harbor, Wash.

• Overall, Puerto Rico's population has been decreasing since 2010. The Commonwealth total resident population decreased by 314,850 (or 8.4 percent) since 2010 to 3,411,307 on July 1, 2016.
• San Juan experienced the largest numeric decrease in population of any municipio, losing 8,497 residents between July 1, 2015 and July 1, 2016, followed by Bayamón (-4,448 residents) and Ponce (-3,748 residents).
• Of Puerto Rico's 78 municipios, only Gurabo experienced growth between July 1, 2015, and July 1, 2016, gaining 56 residents (an increase of 0.1 percent).
• All other municipios experienced a decline in population. The fastest-declining municipios were Peñuelas, Lares and Guánica, featuring a decline of 2.7 percent each.

To find where people are leaving from and moving to, visit Census Flows Mapper.

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The Census Bureau develops county, metro area and micro area population estimates by measuring population change since the most recent census. The Census Bureau uses births, deaths, administrative records and survey data to develop estimates of population. For more detail regarding the methodology, see <www.census.gov/programs-surveys/popest/technical-documentation/methodology.html>.

The Office of Management and Budget's statistical area delineations (for metro and micro areas) are those issued by that agency in July 2015. Metro areas contain at least one urbanized area of 50,000 or more population, and micro areas contain at least one urban cluster of at least 10,000 (but less than 50,000) population. Both metro and micro areas consist of one or more whole counties or county equivalents. Some metro and micro area titles may be abbreviated in the text of the news release. Full titles are shown in the tables.