Gualeguaychú, city, southeastern Entre Ríos provincia (province), northeastern Argentina. It is located on the Gualeguay River near the border with Uruguay. Cattle, poultry, and grains from the agricultural and pastoral hinterland are processed in the city. It is also a regional cultural centre, housing a museum of natural history and fine arts. Buenos Aires, to the south, can be reached by rail, highway, and river. Pop. (2001) 74,164; (2010 est.) 80,100.