Marin County had 262,321 residents at the April 2020 Census, and the Census Bureau’s July 2024 estimate put the population at 256,400, a decline of about 2.3%. The Census Bureau’s 2025 estimate is lower still, at 253,694. Marin is one of the less populous Bay Area counties. It has seen little growth for decades because new housing construction is heavily restricted. censusdatacommons
The population skews older. The median age in Marin is about 48, roughly 25% higher than the California median. That has real estate consequences: censusreporter
- A large share of Marin homes are owned by long-term residents with low Prop 13 tax bases.
- Many properties pass through estates and trusts rather than conventional sales.
- Date-of-death appraisals for step-up in basis and Prop 19 transfers are common here.
The largest population centers are San Rafael, at about 60,000, and Novato, at about 52,000. Most other towns have fewer than 15,000 residents.
