A decade of population growth and decline in US counties

A decade of population growth and decline in US counties

There are a number of factors that determine how much the population of an area changes.

If an area sees a high number of migrants, along with a high birth rate and low death rate, its population is bound to increase over time. On the other hand, if more people are leaving the area than entering it and the area’s birth rate is low, its population will likely decrease.

Which parts of the United States are growing the fastest, and which places are seeing their population decline?

This map, using data from the US Census Bureau, shows a decade of population movement across US counties, painting a detailed picture of US population growth between 2010 and 2020.

Counties with the highest population growth from 2010 to 2020

To calculate population estimates for each county, the US Census Bureau performs the following calculations:

Base population of a county → plus births → minus deaths → plus migration = new population estimate

From 2010 to 2020, Maricopa County in Arizona experienced the largest increase in its population estimate. In a decade, the county has won 753 898 residents. Here are the counties that have seen the largest population increases:

Phoenix and surrounding areas have grown faster than any other major city in the country. The area’s sunny climate and amenities are popular with retirees, but another draw is the housing affordability. Families from the more expensive markets, California in particular, are moving to the city in droves. This is a trend that has caught on in the pandemic era as more people have moved to remote and hybrid work situations.

Texas counties also saw strong growth, with five of the top 10 winners located in the state of Texas. A big draw to Texas is its relatively affordable housing market. In 2021, the average home price in the state was $172,500—$53,310 below the national average.

Counties with the largest population declines from 2010 to 2020

On the other end of the spectrum, here’s a look at the top 10 counties that saw the biggest population declines over the decade:

The largest declines occurred in counties along the Great Lakes, including Cook County (which includes the city of Chicago) and Wayne County (which includes the city of Detroit).

For many of these counties, especially those in America’s “Rust Belt,” population declines during this period were a continuation of decades-long trends. Wayne County is an extreme example of this trend. From 1970 to 2020, the region lost a third of its population.

US population growth in percent (2010-2020)

While the map above is excellent for showing where the greatest number of Americans have migrated, it minimizes large changes in counties with smaller populations.

For example, McKenzie County in North Dakota, with a 2020 population of barely 15,242, was the fastest growing U.S. county over the past decade. That of the county 138% the increase was driven primarily by the Bakken oil boom in the region. Texas’ high-growth counties also grew as new energy sources were extracted in rural areas.

Counties across the country are evenly split between population growth and decline, and clear patterns are emerging.

Pandemic demographic changes

More recent demographic changes reflect longer-term trends. During the COVID-19 pandemic, many of the counties that saw the largest population increases were located in high-growth states like Florida and Texas.

Below are the 20 counties that grew the most from 2020 to 2021.

Many of these counties are located next to major cities, reflecting a shift to suburbs and larger living spaces. However, as COVID-19 restrictions ease and the pandemic housing boom wanes due to rising interest rates, it remains to be seen if suburban displacement will continue or if people will begin to migrate to city centers.