San Mateo is mostly suburban, with some areas of urban development as well. The population is 771,410. Median household income is almost $110,000, and the median home value is $1,347,500. Redwood City is the county seat.

San Mateo County covers most of the San Francisco Peninsula and is part of the greater San Francisco area. San Francisco International Airport is at its northern end, and Silicon Valley begins at the southern end of the county. Beaches are on both east and western borders, and the Santa Cruz Mountains run along its length.

San Mateo County was formed in 1856 after San Francisco County, one of the state's 18 original counties since California's statehood in 1850, was split apart. The Japanese first arrived in San Mateo county and were part of a group guided by Ambassador Tomomi Iwakura back in 1872.There were a number of all male Japanese students who came to San Mateo to learn English and many other helpful skills to bring back to Japan.