The number of young people on the Midpeninsula is shrinking, even as the overall population grows, mirroring a trend throughout California, recently released data from the 2020 U.S. Census shows. The children and teens are also becoming increasingly non-white, although many towns remain far more racially homogeneous than the region overall.

Santa Clara County saw the number of people under 18 drop by 5.4% between 2010 and 2020 (from 429,545 to 406,542), even as the total population increased by 8.7%. In San Mateo County, there are now 3.5% fewer children than a decade ago, decreasing from 159,772 to 154,206, despite a 6.4% increase in the overall number of people living in the county.

The region isn't alone in seeing a smaller number of young people, even as the broader population swells. Statewide, the total number of children has dropped 6.3% over the past 10 years, even as the overall population has grown 6.1%.

With the overall population increasing and number of young people decreasing, the share of Santa Clara and San Mateo counties residents who are under 18 has dropped. In 2010, 24.1% of Santa Clara County residents and 22.2% of San Mateo County residents were under 18. Today, those shares are 21% and 20.2%, respectively. Statewide, the share of young people has dropped from 25% to 22%.

A few local towns — notably Mountain View — did manage to see an uptick in their number of young residents, but those increases were generally overshadowed by larger jumps in the overall population within those areas.

Among the children and teens living on the Midpeninsula, the share identifying as Asian increased substantially, as did those selecting more than one racial group. The portion of white youth dropped, as, to a lesser extent, did the share of Hispanic young people.

The census is conducted every 10 years and collects data on the U.S. population that is used for a variety of purposes, including congressional redistricting. The information gathered includes the total number of people living in given geographic areas, as well as their race and whether they are an adult.

Race and ethnicity data is collected on the census using two questions: one asks if the respondents identify as Hispanic or Latino; the second asks them to pick their race, which may include selecting multiple options. Hispanic or Latino does not appear on that list.

In this article and its accompanying graphics, people who identified as Hispanic or Latino are listed as a single category. All other categories are made up only of those who selected "not Hispanic or Latino."

Countywide changes

Asian people now make up the largest share of those under 18 living in Santa Clara County, while Hispanic people remain the plurality of San Mateo County residents, despite increases in the Asian population.

Today, 36.8% of Santa Clara County young people identify as Asian, 33% as Hispanic, 19.7% as white and 7.6% as more than one racial group. In San Mateo County, 32.5% of young people identify as Hispanic, 27.9% as white, 25.7% as Asian and 10.4% as two or more races. Much smaller shares in both counties identify as other racial groups, including Black and Pacific Islander.

Compared to adults, young people in both counties are substantially less likely to be white. Just 19.7% of those under 18 in Santa Clara County are white, compared with 31.1% of the adult population. White people make up 27.9% of youth in San Mateo County, compared with 38.2% of adults.

On the flip side, young people are more likely to be Hispanic or multiracial than adults.

In Santa Clara County, more than double the share of young people (7.6%) is multiracial compared to adults (3.1%). In San Mateo County, it's nearly three times the share, with 10.4% of young people picking more than one racial group, compared with 3.8% of adults.

Roughly a third (33%) of Santa Clara County young people are Hispanic, versus 23.1% of adults. In San Mateo County, 32.5% of youth are Hispanic, compared to 23.2% of adults.

Taking a closer look

With few exceptions, Midpeninsula cities grew in the last decade, but none saw their share of young people keep up. A few cities have managed to eke out increases in the number of people under 18, but without exception, these cities saw a larger increase in their overall population.

Mountain View had the most notable increase in its youth population, with an 8.7% jump, but the city's total population jumped 11.2%, which was one of the largest increases on the Midpeninsula. That meant the portion of the overall population that's under 18 still dropped slightly, from 19.7% to 19.3%.

Cities like Palo Alto and Los Altos saw an essentially flat number of young people, even as their overall populations jumped. Palo Alto saw a 0.8% drop in the number of youth, while the overall population increased 6.5%. Los Altos overall increased 9.1%, while the number of youth rose just 0.19%.

Many cities saw more substantial drops in the number of children and teens. In East Palo Alto, the change was dramatic, with the number of youth plummeting 15%, even as the overall population grew 6.7%.

Redwood City grew by 9.7% but saw a 5.6% drop in its number of youth. Atherton grew 4% but by 2020 had 11.7% fewer youth. Woodside's population stayed roughly flat, with a 0.42% increase, while the number of young people dropped 12.9%.

North Fair Oaks, an unincorporated area near Redwood City was one of the only places on the Midpeninsula to see its overall population drop, with a decrease of 4.5%, but its youth population plunged far further, dropping 17.6%.

Racial breakdown, city by city

Although Santa Clara and San Mateo Counties overall are racially diverse, many individual cities and areas in the Midpeninsula remain far more racially homogenous.

In cities like Atherton, Portola Valley and Woodside, over 60% of those under 18 are white, which is far higher than the 27.9% of that age group that's white in San Mateo County overall. Places like East Palo Alto and North Fair Oaks, on the other hand, have a population that is nearly 80% Hispanic.

In Santa Clara County, 33% of youth are Hispanic, yet Palo Alto (10.1%), Los Altos (6.3%) and Los Altos Hills (5.9%) all have far smaller shares of Hispanic young people. They each have a substantially higher share of white youth than the county overall.

A few cities have a racial composition of young people that's more in line with its county. That includes Mountain View, where 23.9% of those under 18 are Hispanic, 32% are white, 29.8% are Asian and 12.3% are multiracial.