Buenos Aires, a maritime province of Argentina, South America, bounded N. by the province of Santa Fé and Entre Rios, E. by the latter, the La Plata estuary, and the Atlantic, S. by the Atlantic, and W. by the territories (gobernaciones) of Rio Negro and Las Pampas, and the provinces of Córdoba and Santa Fé. Its area is 117,812 sq. m., making it the largest province of the republic. It is also the most populous, even excluding the federal district, an official estimate of 1903 giving it a population of 1,251,000. Although it has a frontage of over 900 m. on the La Plata and the Atlantic, the province has but few good natural ports, the best being Bahia Blanca, where the Argentine government has constructed a naval port, and Ensenada (La Plata), where extensive artificial basins have been constructed for the reception of ocean-going steamers. San Nicolas in the extreme north has a fairly good river port, while at Buenos Aires a costly artificial port has been constructed.

In its general aspect the province forms a part of the great treeless plain extending from the Atlantic and La Plata estuary westward to the Andes. A fringe of small tangled wood covers the low river banks and delta region of the Paraná between San Nicolas and Buenos Aires; thence southward to Bahia Blanca the sea-shore is low and sandy, with a zone of lagoons and partially submerged lands immediately behind. The south-eastern and central parts of the province are low and marshy, and their effective drainage has long been an urgent problem. Two ranges of low mountains extend partly across the southern part of the province - the first from Mar del Plata, on the coast, in a north-east direction, known at different points as the Sierra del Volcan (885 ft.), Sierra de Tandil (1476 ft.), and Sierra Baya, and the second and shorter range nearer Bahia Blanca, having the same general direction, known at different points as the Sierra Pillahuinco and Sierra de la Ventana (3543 ft.). The country is well watered with numerous lakes and small rivers, the largest river being the Rio Salado del Sud, which rises near the north-western boundary and flows entirely across the province in a south-easterly direction with a course of about 360 m.

The Rio Colorado crosses the extreme southern extension of the province, a distance of about 80 m., but its mouth is obstructed, and its lower course is subject to occasional disastrous inundations.

Cattle-raising naturally became the principal industry of this region soon after its settlement by the Spaniards, and sheep-raising on a profitable basis was developed about the middle of the 19th century. Toward the end of that century the exports of wool, live-stock and dressed meats reached enormous proportions. There is a large export of jerked beef (tasajo) to Brazil and Cuba, and of live-stock to Europe, South Africa and neighbouring South American republics. Much attention also has been given to raising horses, asses, mules, swine and goats, all of which thrive on these grassy plains. Butter and cheese-making have gained considerable prominence in the province since 1890, and butter has become an article of export. Little attention had been given to cereals up to 1875, but subsequently energetic efforts were made to increase the production of wheat, Indian corn, linseed, barley, oats and alfalfa, so that by the end of the century the exports of wheat and flour had reached a considerable value. In 1895 there were 3,400,000 acres under cultivation in the province, and in 1900 the area devoted to wheat alone aggregated 1,960,000 acres.

Fruit-growing also has made good progress, especially on the islands of the Paraná delta, and Argentine peaches, pears, strawberries, grapes and figs are highly appreciated.

The navigation of the Paraná is at all times difficult, and is impossible for the larger ocean-going steamers. The greater part of the trade of the northern and western provinces, therefore, must pass through the ports of Buenos Aires and Ensenada, at which an immense volume of business is concentrated. All the great trunk railways of the republic pass through the province and converge at these ports, and from them a number of transatlantic steamship lines carry away the products of its fertile soil. The province is also liberally supplied with branch railways. In the far south the new port of Bahia Blanca has become prominent in the export of wool and wheat.

The principal cities and towns of the province (apart from Buenos Aires and its suburbs of Belgrano and Flores) are its capital La Plata; Bahia Blanca, San Nicolas, a river port on the Paraná 150 m. by rail north-west of Buenos Aires, with a population (1901) of 13,000; Campana (pop. 5419 in 1895), the former river port of Buenos Aires on one of the channels of the Paraná, 51 m. by rail north-west of that city, and the site of the first factory in Argentina (1883) for freezing mutton for export; Chivilcoy, an important interior town, with a population (1901) of 15,000; Pergamino (9540 in 1895), a northern inland railway centre; Mar del Plata, a popular seaside resort 250 m. by rail south of Buenos Aires; Azul (9494), Tandil (7088), Chascomús (5667), Mercedes (9269), and Barracas al Sud (10,185), once the centre of the jerked beef industries.

The early history of the province of Buenos Aires was a struggle for supremacy over the other provinces for a period of two generations. Its large extent of territory was secured through successive additions by conquest of adjoining Indian territories south and west, the last additions being as late as 1879. Buenos Aires became a province of the Confederation in 1820, and adopted a constitution in 1854, which provides for its administration by a governor and legislature of two chambers, both chosen by popular vote. An unsuccessful revolt in 1880 against the national government led to the federalization of the city of Buenos Aires, and the selection of La Plata as the provincial capital, the republic assuming the public indebtedness of the provinces at that time as an indemnification. Before the new capital was finished, however, the province had incurred further liabilities of ten millions sterling, and has since then been greatly handicapped in its development in consequence.

(A. J. L.)