Biritiba Mirim is a municipality located in the state of São Paulo, Brazil. It is situated within the Metropolitan Region of São Paulo and covers a total area of 317.41 km² (122.55 sq mi). The municipality has a population of 32,936 residents.
The geographic boundaries of Biritiba Mirim are defined by neighboring municipalities: Guararema lies to the north, Salesópolis to the east, Bertioga to the south, and Mogi das Cruzes to the west and northwest.