Rio Grande (rēˈŏ gränˈdĭ) [key], city (1991 pop. 172,422), Rio Grande do Sul state, S Brazil, on the Rio Grande River at the outlet of the Lagoa dos Patos (a tidal lagoon) to the Atlantic Ocean. It is an important outport for the city of Pôrto Alegre on the northern end of the lagoon. Rio Grande has oil refineries and factories producing foodstuffs, leather, and tires. The city was founded in 1737.