Portola Valley is an incorporated town in San Mateo County, California, United States. The population was 4,462 at the 2000 census. It was named for Spanish explorer Gaspar de Portola, who led the first party of Europeans to explore the San Francisco Peninsula, in 1769. Portola Valley is one of the top forty wealthiest towns in the United States of America, with a median household income of $158,217 a year. Within the State of California, Portola Valley is ranked as the sixth wealthiest place. The zip code 94028, which encompasses the whole of Portola Valley, has the 37th most expensive housing prices within the country according to Forbes Magazine 2009.