San Leandro is a city in Alameda County, California, United States. It is located in the East Bay of the San Francisco Bay Area; between Oak…San Leandro is a city in Alameda County, California, United States. It is located in the East Bay of the San Francisco Bay Area; between Oakland to the northwest, and Ashland, Castro Valley, and Hayward to the southeast. The population was 91,008 as of the 2020 census.