Três Rios is a municipality located in the Brazilian state of Rio de Janeiro. As of 2020 its population was an estimated 82,142 inhabitants, and its area is around 322 square kilometres (124 sq mi). The current mayor of Três Rios is Joacir Barbaglio Pereira of the Liberal Party, elected in 2020 to a four-year term.

The Paraíba do Sul, or simply termed Paraíba, is a river in southeast Brazil. It flows 1,137 km (706 mi) west to northeast from its farthest source at the source of the river Paraitinga to the sea near Campos dos Goytacazes. The river receives its name when it meets the river Paraibuna at the Paraibuna dam.