The U.S. population in 2020 was older and had fewer children under age 5 than in 2010 or 2000, according to the 2020 Census Demographic and Housing Characteristics (DHC) data released today.

The baby boom generation (born 1946-1964) and millennials (born 1982-2000) — the two largest U.S. cohorts in 2020 — both continued to age over the past two decades. At the same time, smaller cohorts of children were born from 2010 to 2020.

The 2020 Census DHC data allows us to examine the age and sex composition of the nation and smaller geographies such as states, counties, metropolitan areas and micropolitan areas. It also shows that the age and sex compositions of different geographies do not always follow the same pattern of change over time. 

Figure 2 shows three population pyramids for the United States: 2000, 2010 and 2020. Both the size and shape of the nation’s population changed during the century’s first two decades.

The pyramid was larger in 2020 than it was in either 2010 or 2000. This reflects the growth in the U.S. population: 331.4 million people in 2020, up 22.7 million (7.4%) from the 308.7 million in 2010. Between 2000 and 2010, the population grew by 27.3 million (9.7%) from 281.4 million people.

The U.S. population also aged since 2000. The baby boom cohort moved up the pyramid, from 36-to-54-year-olds in 2000 to 46-to-64-year-olds in 2010 and 56-to-74-year-olds in 2020. The millennials were mostly in their teens and 20s in 2010 but young adults (in their 20s and 30s) a decade later.

At the same time, the base of the pyramid representing children under age 5 got smaller in 2020, reflecting a recent decrease in the number of births in the United States.

While the population pyramid for the United States tells us about the nation, sex and age composition can vary significantly at the state, county, metropolitan, and micropolitan levels. In the following sections, we highlight a handful of geographies to illustrate interesting changes in the age and sex compositions of various communities over the past three censuses.

For example, the triangular shape of Utah’s population pyramid, with a broader base and narrower top, shows Utah had a relatively young population (Figure 3). Indeed, in 2020, Utah was the nation’s youngest state, with the lowest median age (31.3 years) and the country’s highest share (29.0%) of population under age 18.

But Utah’s population both grew and aged during the century’s first two decades. The state’s population rose 46.5% (from 2.2 million in 2000 to 3.3 million in 2020). At the same time, the state’s median age increased by 4.2 years (from 27.1 to 31.3) and the share of its population age 65 and over increased (from 8.5% in 2000 to 11.7% in 2020). 

Over the past decade, Denver County had the largest population increase of any county in Colorado, adding more than 115,000 people, from 600,158 in 2010 to 715,522 in 2020 (Figure 4). 

While its median age increased by less than half a year (from 33.7 to 34.1), its young adult population grew with an especially large (39.6%) increase in the population of 25-to-34-year-olds.

From 2010 to 2020, the county’s under-18 population increased slightly but its share of children declined from 21.5% in 2010 to 18.8% in 2020. 

Between 2010 and 2020, Williams County, North Dakota was one of the nation’s fastest growing counties, with its population increasing by 82.8%, from 22,398 in 2010 to 40,950 in 2020 (Figure 5). At the same time, its median age decreased by 7.4 years (from 39.0 to 31.6 years).

This lower median age coincided with a large increase in the numbers of working-age people (especially males) in the county, due at least in part to migration for employment opportunities in the oil industry. In 2020, each single year of age between 26 and 37 years had over 400 more people than it did in 2010.

There was also a large increase in the county’s child population over the decade. The population under age 18 more than doubled (from 5,165 in 2010 to 11,157 in 2020) to become over a quarter (27.2%) of the county, with over 300 more children at every year of age below 10.

Unlike the counties above, Alexander County, Illinois experienced a decrease in size and a relative increase in its older population from 2000 to 2020 (Figure 6).

The county’s population fell 14.1% from 9,590 in 2000 to 8,238 in 2010 and declined another 36.4% to 5,240 in 2020. This loss of nearly half its population over two decades is reflected in a noticeably smaller pyramid in 2020 than in 2000. During the same period, Alexander County’s median age increased by 11.1 years (from 38.0 to 49.1).

Between 2000 and 2020, the number of children age 17 and younger decreased 60% while the number of older adults 65 and over decreased only 20%. As a result, children became a smaller share of the county’s population (decreasing from 25.8% in 2000 to 19.1% in 2020) while older adults became a larger share (increasing from 16.9% in 2000 to 24.8% in 2020).

Together these figures represent a striking shift from dependent children to a dependent older population. 

Other geographies grew older over time due primarily to large increases in their older populations.

The fastest-growing U.S. metropolitan area between 2010 and 2020 was The Villages, Florida. This metro area’s population grew by 38.9% in this period (from 93,420 in 2010 to 129,752 in 2020), and 143.2% between 2000 and 2020 (Figure 7).

This metro area, home to an age-restricted retirement community, had the oldest median age in 2020 of any metro area in the nation (68.5 years).

The growth of the older population is evidenced by the widening bars at age 60 years and over and coincides with an increase in the number of people age 65 and over from 14,618 in 2000 (27.4% of the county) to 76,372 in 2020 (58.9%).