Buenos Aires, provincia (province), eastern Argentina. It lies south of the Paraná River and southeast of the Río de la Plata (which forms the border with Uruguay) and extends westward from the Atlantic Ocean to include the major part of the humid Argentine Pampas, a vast grass-covered plain. The province, which surrounds the Federal District and the city of Buenos Aires, includes Martín García Island. La Plata, southeast of Buenos Aires city, is the provincial capital.

The largest and most-populated of the provinces, it is the cultural and economic centre of Argentina. One main river, the Salado, crosses the province (northwest–southeast) for a distance of 360 miles (580 km). In the south, two low mountain ranges, the Sierra del Tandil and the Sierra de la Ventana, extend inland from the coast in northwesterly directions.

During colonial times the region was lightly settled but produced hides from the vast herds of cattle and horses that ran wild on the Pampas. The inhabitants supported separation from Spain in 1810, but throughout most of the 19th century there was continued internal strife during the efforts to organize the nation. Provincial status was attained in 1862. The city of Buenos Aires became the site of the national government in 1880, and the provincial authorities moved their administration to La Plata. About the same time, the Pampa Indians were decimated by the Argentine military. The period of peace that followed, as well as an influx of foreign immigrants, stimulated economic development.

The late 19th and early 20th centuries witnessed the expansion of cattle raising and of wheat, corn (maize), and alfalfa farming as major sources of income for both domestic and European markets. Although Buenos Aires province ranks first in the republic for the number and quality of its livestock, an increasing area has been given over to crops. Livestock raising is concentrated in the coastal area below the Federal District, extending inland for 150 miles (240 km) and southward to Mar del Plata. A broad band running north and south through the province and growing wider in the southern coastal region is devoted to wheat. Corn (maize) is raised in the north, while around the federal district, for a radius of some 50 miles (80 km), are intensive truck gardens that supply the urban population with fresh fruits and vegetables. Industry and transportation systems are concentrated in the federal capital of Buenos Aires and its suburbs, but Bahía Blanca, Mar del Plata, and La Plata are also important industrial and communication centres. Area 118,754 square miles (307,571 square km). Pop. (2001) 13,827,203; (2010) 15,625,084.