Belmont is a city in San Mateo County, California, United States. It is a small suburb in the San Francisco Bay Area, located half-way down the San Francisco Peninsula between San Mateo and San Carlos. The population was 25,123 at the 2000 census.

Belmont is mostly made up of residential housing and retail stores. During the 1990s housing demand (and prices) increased dramatically, in large part due to the growth of the nearby headquarters of Oracle Corporation.

Ralston Hall, built around a villa formerly owned by Count Cipriani, an Italian aristocrat, by Bank of California founder William Chapman Ralston, on the campus of Notre Dame de Namur University is a historic landmark.

Carlmont High School is located in Belmont.

Belmont is located at 37°31′5″N, 122°17′30″W (37.518087, -122.291673) GR1 .

According to the United States Census Bureau, the city has a total area of 11.7 km² (4.5 mi²). 11.7 km² (4.5 mi²) of it is land and 0.52% is water.