Guapiaçu is a municipality in the state of São Paulo, Brazil. It is located in the north/northwest portion of the state, about 17 kilometres (11 mi) from the city of São José do Rio Preto.
According to the Brazilian Institute of Geography and Statistics (IBGE), the municipality had a population of 21,775 in 2020, distributed across an area of 326 square kilometres (126 sq mi).