São Caetano do Sul is a city in São Paulo state in Brazil. It is part of the Metropolitan Region of São Paulo. The population is 161,957 in an area of 15.33 km2. It is the city with the highest per capita income in Brazil and it also has the highest Human Development Index. It is intensely conurbated with São Paulo, Santo André and São Bernardo do Campo, causing the physical limits between cities to be lost.