Little Brother is set in various places in San Francisco, but focuses mainly on the Mission District, where Marcus and most of his friends go to school. The specific area in San Francisco in which Marcus resides is actually called Potrero Hill, and his house is one of San Francisco’s storied “Painted Ladies”.
Marcus is also mentioned as a student of Cesar Chavez High, which automatically makes him one of the city’s most watched people. Chavez High has several gait recognition and classroom cameras.
Also, Little Brother is set in the somewhat near future- one can tell by the technology and hacks used such as the Xbox Universal and Paranoid Linux.