Atherton is an incorporated town in San Mateo County, California, United States. Its population was 7,159 as of 2013. In 1990, Atherton was ranked as having the highest per capita income among U.S. towns with a population between 2,500 and 9,999, and it is regularly ranked among the most expensive ZIP Codes in the country.

The 2010 United States Census reported that Atherton had a population of 6,914. The population density was 1,369.5 people per square mile (528.8/km²). The racial makeup of Atherton was 5,565 (80.5%) White, 75 (1.1%) African American, 7 (0.1%) Native American, 911 (13.2%) Asian, 45 (0.7%) Pacific Islander, 95 (1.4%) from other races, and 216 (3.1%) from two or more races. Hispanic or Latino of any race were 268 persons (3.9%).

The census reported that 6,529 people (94.4% of the population) lived in households, 385 (5.6%) lived in non-institutionalized group quarters, and 0 (0%) were institutionalized.

There were 2,330 households, out of which 787 (33.8%) had children under the age of 18 living in them, 1,755 (75.3%) were opposite-sex married couples living together, 109 (4.7%) had a female householder with no husband present, 48 (2.1%) had a male householder with no wife present. There were 34 (1.5%) unmarried opposite-sex partnerships, and 15 (0.6%) same-sex married couples or partnerships. 321 households (13.8%) were made up of individuals and 178 (7.6%) had someone living alone who was 65 years of age or older. The average household size was 2.80. There were 1,912 families (82.1% of all households); the average family size was 3.03.

The population was spread out with 1,543 people (22.3%) under the age of 18, 579 people (8.4%) aged 18 to 24, 966 people (14.0%) aged 25 to 44, 2,264 people (32.7%) aged 45 to 64, and 1,562 people (22.6%) who were 65 years of age or older. The median age was 48.2 years. For every 100 females, there were 96.6 males. For every 100 women age 18 and over, there were 95.3 men.

The median income for a household in the town was in excess of $250,000, the highest of any place in the United States. The per capita income for the town was $128,816. About 2.9% of families and 5.1% of the population were below the poverty line, including 5.6% of those under age 18 and 5.4% of those age 65 or over.

There were 2,530 housing units at an average density of 501.1 per square mile (193.5/km²), of which 2,116 (90.8%) were owner-occupied, and 214 (9.2%) were occupied by renters. The homeowner vacancy rate was 1.6%; the rental vacancy rate was 3.9%. 5,921 people (85.6% of the population) lived in owner-occupied housing units and 608 people (8.8%) lived in rental housing units.

Forbes ranked Atherton as second on its list of America’s Most Expensive ZIP Codes in 2010, listing median house price as over $2,000,000.

