As with most other towns in Marin county, San Anselmo is known for its security and affluence. Like many other cities in the San Francisco Bay Area, San Anselmo is named after a Catholic saint. "San Anselmo" is Spanish for Saint Anselm.
As of the census of 2000, there are 12,378 people, 5,267 households, and 3,191 families residing in the town. The population density is 1,737.9/km² (4,506.5/mi²). There are 5,408 housing units at an average density of 759.3/km² (1,968.9/mi²). The racial makeup of the town is 91.62% White, 1.05% African American, 0.40% Native American, 2.92% Asian, 0.12% Pacific Islander, 0.95% from other races, and 2.93% from two or more races. 4.14% of the population are Hispanic or Latino of any race.
There are 5,267 households out of which 30.2% have children under the age of 18 living with them, 48.5% are married couples living together, 8.7% have a female householder with no husband present, and 39.4% are non-families. 28.7% of all households are made up of individuals and 7.3% have someone living alone who is 65 years of age or older. The average household size is 2.30 and the average family size is 2.84.
In the town the population is spread out with 21.8% under the age of 18, 4.4% from 18 to 24, 31.4% from 25 to 44, 31.1% from 45 to 64, and 11.3% who are 65 years of age or older. The median age is 41 years. For every 100 females there are 89.2 males. For every 100 females age 18 and over, there are 85.4 males.
The median income for a household in the town is $71,488, and the median income for a family is $86,528. Males have a median income of $61,172 versus $47,170 for females. The per capita income for the town is $41,977. 5.1% of the population and 2.5% of families are below the poverty line. Out of the total people living in poverty, 1.7% are under the age of 18 and 3.1% are 65 or older.