Mapped: The Median Age in Every U.S. County

Today, highly detailed maps of our planet’s surface are just a click away.

In times past, however, access to information was much more limited. It wasn’t until the 1800s that comparison diagrams and maps became widely accessible, and people found new ways to learn about the world around them.

The image above, published by J.H. Colton in 1849, is believed to be the first edition of the iconic mountains and rivers infographic map. This comparison chart concept would see a number of iterations over the years as it appeared in Colton’s world atlases.

Inspiring a Classic Infographic Map

A seminal example of this style of infographic was produced by Alexander von Humboldt in 1805. The diagram below is packed with information and shows geographical features in a way that was extremely novel at the time.

In 1817, the brothers William and Daniel Lizars produced the first comparative chart of the world’s mountains and rivers. Breaking up individual natural features into components for comparison was a very innovative approach at that time, and it was this early French language prototype that lead to the Colton’s versions we’re familiar with today.

Digging into the Details

As is obvious, even at first glance, there is a ton of detail packed into this infographic map.

Firstly, rivers are artificially straightened and neatly arranged in rows for easy comparison. Lakes, mountain ranges, and cities are all labeled along the way. This unique comparison brings cities like New Orleans and Cairo side by side.

Of course, this visualization was based on the best available data at the time. Today, the Nile is widely considered to be the world’s longest river, followed by the Amazon and Yangtze.

Over on the mountain side, there are more details to take in. The visualization includes volcanic activity, notes on vegetation, and even the altitude of selected cities and towns.

Above are a few of South America’s high-altitude population centers, including La Paz, which is the highest-elevation capital city in the world.

In the legend, many of the mountains are simply named “peak”. While this generic labeling might seem like a throwback to a time when the world was still being explored, it’s worth noting that today’s second tallest mountain is still simply referred to as K2.

What details do you notice while exploring this iconic infographic map?

A Decade of Population Growth and Decline in U.S. Counties

There are a number of factors that determine how much a region’s population changes.

If an area sees a high number of migrants, along with a strong birth rate and low death rate, then its population is bound to increase over time. On the flip side, if more people are leaving the area than coming in, and the region’s birth rate is low, then its population will likely decline.

Which areas in the United States are seeing the most growth, and which places are seeing their populations dwindle?

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

Counties With The Biggest Population Growth from 2010-2020

To calculate population estimates for each county, the U.S. Census Bureau does the following calculations:

 
From 2010 to 2020, Maricopa County in Arizona saw the highest increase in its population estimate. Over a decade, the county gained 753,898 residents. Below are the counties that saw the biggest increases in population:

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

Texas counties saw a lot of growth as well, with five of the top 10 gainers located in the state of Texas. A big draw for Texas is its relatively affordable housing market. In 2021, average home prices in the state stood at $172,500—$53,310 below the national average.

Counties With The Biggest Population Drops from 2010-2020

On the opposite end of the spectrum, here’s a look at the top 10 counties that saw the biggest declines in their populations over the decade:

The largest drops happened 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, particularly those in America’s “Rust Belt”, population drops over this period were a continuation of decades-long trends. Wayne County is an extreme example of this trend. From 1970 to 2020, the area lost one-third of its population.

U.S. Population Growth in Percentage Terms (2010-2020)

While the map above is great at showing where the greatest number of Americans migrated, it downplays big changes in counties with smaller populations.

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

The nation’s counties are evenly divided between population increase and decline, and clear patterns emerge.

Pandemic Population Changes

More recent population changes reflect longer-term trends. During the COVID-19 pandemic, many of the counties that saw the strongest 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 large cities, reflecting a shift to the suburbs and larger living spaces. However, as COVID-19 restrictions ease, and the pandemic housing boom tapers off due to rising interest rates, it remains to be seen whether the suburban shift will continue, or if people begin to migrate back to city centers.