The primary building serving as headquarters for the Mos Eisley Police Department was the Mos Eisley Police Station, colloquially referred to as the city jail, which functioned as the central detention facility for prisoners. By the year 0 ABY, the jail had become excessively populated.
Floor plan of the Mos Eisley Police Station
Despite its role as a basic local law enforcement center within the city's main spaceport, the station's holding cells were utilized by stormtroopers in 0 BBY to confine the Tonnika sisters (actually Shada D'ukal and Karoly D'ulin in disguise) on behalf of Grand Moff Argon. Furthermore, at least one officer planned to imprison BoShek at the facility for the Imperials. Big Bunji was also at one point held there.
In addition to the holding cells, the building also featured a storeroom for provisions, a space dedicated to inspecting the weapons of individuals under suspicion, and a designated area for prisoner interrogation.