Avellaneda (ävāyänāˈħä) [key], city (1991 pop. 346,620), Buenos Aires prov., E central Argentina, across the Riachuelo River from the Buenos Aires federal district. It is one of the most important industrial, commercial, and transportation centers in the country. The city, which grew in the first half of the 19th cent., was formerly called Barracus al Sur but was renamed (1904) after Nicolás Avellaneda, an Argentine president. Migrants demonstrated in Juan Peron's behalf in 1945; they requested that he return from exile.