Río Segundo, sometimes abbreviated as Río 2º, is a city in the province of Córdoba, Argentina. It lies near the geographical center of the country, built on the banks of the Río Segundo, roughly 40 kilometres (25 mi) east-southeast of the provincial capital, Córdoba, and about 660 kilometres (410 mi) west-northwest of Buenos Aires. It is the largest city in Río Segundo Department.
The city straddles National Route 9 and a main railway line running between Córdoba and Buenos Aires, giving it a position on one of Argentina's principal transport corridors. Across the river from Río Segundo sits Pilar, a smaller city.