SAN DIEGO — San Diego County became older, faster over the last decade, according to new census data, following a trend of growth to senior populations nationwide that outpaced any other ten-year period in more than a century.

A analysis of new figures from the 2020 census released by the U.S. Census Bureau last week estimated that the share of residents in San Diego County aged 65 or older grew over the last decade, while the share of children and adults in their 20s declined.

Over the last decade, the population of adults older than 65 in San Diego County jumped about 26%, while the number of children under the age of 9 fell about 10%. Young adults aged 20 to 29 also saw a moderate decrease over the last 10 years, declining about 2%.

These trends, combined with a median age jump from 34.6 to 37.1 in the county, mirrored nationwide changes across age demographics that is considered the fastest decadal rate of aging in the last 130 years.

According to experts with the federal agency, this aging was likely driven by America’s two largest age groups: baby boomers and millennials. More people in the baby boomer generation turned 65 or older over the last decade, while millennials pushed farther into their 20s or 30s. Fewer children born in the decade also contributed to the decline.

Changes over the last five years of population estimates — from 2017 to 2021 — also reflected an aging of the population in San Diego County.

Since 2017, the population of adults ages 20 to 29 fell about 6.61%, while the percent of children under the age of five to 9-years-old dropped by 5.27%. Older San Diegans from 60 to 79, on the other hand, saw about 10.75% growth in population size in the last five years.

Despite some of these demographic changes, adults aged 20 to 39 — groups long considered synonymous with parts of the “San Diego lifestyle” — still accounted for the largest share of the county’s population, according to the recent census data.

The U.S. Census Bureau estimates about 3.3 million residents live within San Diego County. About 30% of the population is between the ages of 20 and 39, while 20.9% are under the age of 18 and 19.85% are over the age of 65.

A full breakdown of the San Diego County population shares by age group can be found below:

AgeShare of population in 2021
under 5-911.84%

Census data breaking down demographics and housing characteristics was released last week, after about a two-year delay due to difficulties caused by the pandemic.

The new data fully fleshes out the basic population counts and demographic information previously released in 2020 for the purposes of congressional appointment and legislative redistricting, according to the Census Bureau.