Três Fronteiras (Portuguese meaning the "three frontiers") is a municipality in the state of São Paulo in Brazil. The population in 2004 was 5,180, the density was 33.82/km² and the area is 153.16 km². The elevation is 395 m.
The origin of the name is after the three frontiers of the three states including São Paulo, the three frontiers is actually bounded directly over the Paraná River and another river not far to the west northwest which are also a reservoir. It is linked with a major highway and a superhighway linking the city of São Paulo and the western part of Brazil to the north, a railway and several state highways. Most of the population are farmers.