San Mateo, California, a city in San Mateo County. It lies on San Francisco Bay, 19 miles (31 km) south of downtown San Francisco. San Mateo is a large residential community and a center of commercial flower growing. It has little manufacturing. The San Mateo-Hayward Bridge, completed in 1967, links the city with the east side of the bay. San Mateo was laid out in 1863.