Only 50 U.S. Counties Had Populations Over a Million in 2024

The U.S. has experienced steady population increase over the past few decades. On July 1, 1970, the nation’s population was nearly 204 million. By July 1, 2024, it had grown to over 340 million and many more counties saw their populations swell above one million.

The 23 counties with at least one million people in 1970 were in 11 states: New York (7); California (5); Pennsylvania (2); Texas (2); Florida (1); Illinois (1); Massachusetts (1); Michigan (1); Ohio (1); Washington (1); and Wisconsin (1).

Two more counties ­— Maricopa in Arizona (in 1971) and Oakland in Michigan (in 1979) — had joined the million-plus club during the 1970s while one, Milwaukee in Wisconsin (1977), dipped below the threshold. This brought the total number of million-person counties to 24 by 1980.

By 1990, seven more counties (three in California, two in Texas, and one in both Florida and Minnesota) had crossed the million-person mark. Two counties dropped below it — Erie in New York and Oakland in Michigan — but Oakland recovered, bringing the new total of million-plus counties to 30.

More than three decades later, another 22 counties had gained and two had lost the million-person distinction.

In 2024, Gwinnett County, Georgia, became the latest million-person county, bringing the total to 50 for the first time. These 50 counties spanned 18 states, led by California (10), New York (7) and Texas (7).

Los Angeles County retained the top spot as the nation’s most populous million-person county from 1970 to 2024, growing by 2.7 million (38%) and peaking in 2017.

The nation’s five most populous million-person counties in 2024:

• Los Angeles County, California (population 9,757,179).
• Cook County, Illinois (5,182,617).
• Harris County, Texas (5,009,302).
• Maricopa County, Arizona (4,673,096).
• San Diego County, California (3,298,799).

Gwinnett County was the least populous million-person county and most recent to exceed the one million population threshold, ballooning by 930,199 people or 1,263% to 1,003,869 in 2024 from less than 74,000 in 1970.

The five least populous million-person counties in 2024:

• Gwinnett County, Georgia (population 1,003,869).
• Westchester County, New York (1,006,447).
• Fresno County, California (1,024,125).
• Denton County, Texas (1,045,120).
• Duval County, Florida (1,055,159).

Four counties — Erie, New York; Milwaukee, Wisconsin; St. Louis, Missouri; and Honolulu, Hawaii — were once million-person counties but not anymore.

Erie and Milwaukee counties dropped below the million mark more than 30 years ago. St. Louis and Honolulu counties lost the status within the last five years but remained fewer than 10,000 people shy of the threshold.

Two other counties, Oakland in Michigan and Westchester in New York, swung above and below the one million threshold during the 54-year period but both met the mark last year.

Notably, St. Louis, Honolulu and Westchester counties dipped below the million mark between 2020 and 2022. These declines can partly be attributed to high levels of domestic outmigration during the COVID-19 pandemic.

In 1970, just over 61 million people lived in the 54 counties that ever had more than one million people. By 2024, these counties had gained more than 44 million people, for a total of 105 million.

Despite this large numeric growth, the share of the U.S. population living in these counties stayed consistent (29% to 31% in any given year) from 1970 to 2024.

Some of the counties with more than one million people had gradual population declines since 1970. Among them: Wayne County, Michigan (down 34%); Cuyahoga County, Ohio (down 28%); Allegheny County, Pennsylvania (down 23%); and Philadelphia County, Pennsylvania (down 19%).

One geographical feature of million-person counties is population growth in neighboring counties. After one county reaches a million population, some nearby counties gradually join the million-population club as well. This often happens as a result of people migrating to counties adjacent to million-person counties.

One example is in southern California. Los Angeles, Orange and San Diego counties all had at least one million people in 1970.

Neighboring counties of San Bernardino and Riverside slowly grew throughout the 1970s and 1980s until they both crossed the million-person mark — San Bernardino in 1984 and Riverside in 1989.

Another example is in Texas. Dallas County was a million-person county in 1970 but none of its neighboring counties were.

Dallas County continued growing for decades. By 2024, three of its neighboring counties had also crossed the one-million threshold: Tarrant (in 1984); Collin (2018) and Denton (2023).