Why is this Important?

The size, age, and composition of the population are important indicators for community planning and economic activity. Shifts in the demographic profile such as increased immigration and movement towards younger or older age groups can bring new demands for public services, impact economic growth, and exert pressure on open space or natural resources.

What is a Sustainable State?

In a sustainable state, a community can adapt to changing population dynamics without negatively impacting quality of life or depleting non-renewable natural resources.

Key Findings

  • In 2015, San Mateo County’s population was 753,123, an increase of 7,930 over the year prior. This growth includes a natural increase (number of births minus number of deaths) of 4,589 people and positive net migration (number of people moving in minus people moving out) of 3,099 residents.
  • By 2040, San Mateo County’s population is projected to grow by over 100,000 residents compared to 2015, while the Bay Area is projected to add an additional 1 million people.
  • Between 2014 and 2040, the age profile of the county is expected to change, with the share of residents 65 and older nearly doubling. There is also expected to be significant growth in the Hispanic/Latino population.


  • In 2015, the county population increased substantially by 7,488 from 2014, an 8% increase compared to the low of 699,277 in 2005.
  • The Center for Migration Studies estimates that there were 50,052 undocumented residents in the county in 2013. This estimate is not comparable to the population in the chart above, due the undercount of undocumented residents in the American Community Survey.


  • In 2015, natural increase (number of births minus number of deaths) added 4,589 residents to San Mateo County, 3% lower than the year prior.
  • Net migration is a combination of foreign immigration (legal and unauthorized foreign immigration, as well as residents leaving the county to live abroad), and domestic migration (people moving within the United States to and from San Mateo County). In 2015, the county added 3,438 residents through foreign immigration and lost 339 residents to domestic migration.

ssmc_2016_marchupdate-01Population Growth and Migration, 2015

  • San Francisco County, San Mateo County, and the State of California all lost residents in 2015 to domestic migration (more people moving out of the area to other parts of the U.S. than moving in). High housing costs have forced some residents of the more expensive Bay Area counties to relocate to more affordable areas. All Bay Area counties and the state added population through foreign immigration.



Projected Population Growth, Bay Area Counties, 2015

  • San Mateo County is projected to add approximately 118,503 residents by 2040, while the Bay Area is projected to grow by over 1 million people.
  • Calculations made by the Association of Bay Area Governments (ABAG) and Plan Bay Area project even higher population growth between now and 2040. According to their forecasts, San Mateo County will add 185,000 residents and the Bay Area will grow by 2 million.
  • Planning now for additional housing and transportation to accommodate the region’s growth is essential.

  • As our population ages, the share of residents 65 and older is projected to nearly double. By 2040, nearly one in four county residents is expected to be 65 and older.

  • The composition of the county by race/ethnicity will also change over the next twenty years, with the most pronounced growth expected in the share of total population that is Hispanic/Latino.

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