Inhabited by the native Charrúa people, the site's strategic location on the Salado River made it of interest to Spanish Viceroy Juan José de Vértiz y Salcedo, who established an outpost there in the 1790s as part of a line of defense against raids by displaced natives.
The location became known as El Potroso.

El Potroso was reinforced by a fort by way of an 1826 decree by President Bernardino Rivadavia, and on December 27, 1827, the citadel was established under the command of a veteran of the Argentine War of Independence, Bernardino Escribano, as Fuerte de la Federación.
The advent of Buenos Aires Province Governor Juan Manuel de Rosas led to Escribano's 1829 destitution as commander; though the intervention of an officer, Isidoro Suárez, averted a bloodbath.
Suárez, a veteran of one of the last battles of the War for Independence (the Battle of Junín, in Perú), inadvertently gave the failing settlement its new name by his actions: "Junín."

Political conflict and ongoing Indian raids had all but destroyed Junín by the 1830s, however, and this prompted Governor Rosas to send the remaining settlers provisions and to subsidize crop farming in the surrounding, fertile pampas fields.
This was followed by a pact with Ranquel Chief Santiago Yanquelén, whereby his people would defend Junín against raids by other tribes.
Towards the end of his rule, Rosas appointed José Seguí, among the few Afro Argentines to achieve a commissioned officer's rank, to administer Junín, in 1851.
Seguí was an efficient, though repressive commander, and in 1863, he was assassinated at his nearby ranch.

Rosas' 1852 overthrow resulted in the appointment of a justice of the peace, who initially shared governing duties with the military commander.
 Junín's first general store (Basterreix) opened in 1860, and in 1861, Junín elected its first city council (despite being officially only a fort).
The province designated the area as a county in 1864, and with nearly 2,000 inhabitants, Junín ceases to be categorized as a "fort," and its first municipal master plan was laid out in 1865.

The 1880 arrival of the Central Argentine Railway and that of the Buenos Aires and Pacific Railway (B.A.& P.) in 1884 led to the town's rapid growth.
The National Bank of Argentina had opened a branch there in 1892 and by the 1895 census, Junín was home to over 12,000.
The town largest employer by then was the B.A.& P.'s rail equipment factory, which employed over 1,600.
The City Hall was completed in 1904 and Junín was declared a "city," in 1906.

Junín's steady development over the subsequent decades and setting amid lakes made it a well-known regional tourist destination.
A hunting club was established in 1938, and a fishermen's pier and club on Lake El Carpicho, in 1942.
 The Aero Club Junín (1940) became well-known following the IX International Gliding Competition, in 1963, and the nearby Borchex Municipal Park and Lake Gómez both have become popular weekend destinations since the 1960s; Lake Gómez attracted around 350,000 visitors during the 2006-07 summer season.
Nearby Estancia La Oriental has attracted growing rural tourism to the area, as well.

The city is home to an important Municipal Historical Museum, probably best known for its paleontology hall and its wooly mammoth fossils, and the Ángel María de Rosa Municipal Museum of Art (1944).
In a bid to further diversify the city's economy, an industrial park was authorized north of the city in 1995, and a racetrack, the Autódromo Eusebio Marcilla, was opened in 2003.
The closure of much of Argentina's passenger rail service during the 1990s was partly offset in Junín in part by the purchase of local rail facilities by América Latina Logística, a São Paulo-based rail transport provider operating largely in Argentina, as well as by establishment of the Junín Railworks Cooperative.

The city features numerous cinemas, as well as prominent stage theatres such as the Teatro de la Ranchería (1971).
The city's first institution of higher learning, the Junín Regional University (CURJ), was established in 1990; fused with its
Inhabited by the native Charrúa people, the site's strategic location on the Salado River made it of interest to Spanish Viceroy Juan José de Vértiz y Salcedo, who established an outpost there in the 1790s as part of a line of defense against raids by displaced natives. The location became known as El Potroso.
El Potroso was reinforced by a fort by way of an 1826 decree by President Bernardino Rivadavia, and on December 27, 1827, the citadel was established under the command of a veteran of the Argentine War of Independence, Bernardino Escribano, as Fuerte de la Federación. The advent of Buenos Aires Province Governor Juan Manuel de Rosas led to Escribano's 1829 destitution as commander; though the intervention of an officer, Isidoro Suárez, averted a bloodbath. Suárez, a veteran of one of the last battles of the War for Independence (the Battle of Junín, in Perú), inadvertently gave the failing settlement its new name by his actions: "Junín."
Political conflict and ongoing Indian raids had all but destroyed Junín by the 1830s, however, and this prompted Governor Rosas to send the remaining settlers provisions and to subsidize crop farming in the surrounding, fertile pampas fields. This was followed by a pact with Ranquel Chief Santiago Yanquelén, whereby his people would defend Junín against raids by other tribes. Towards the end of his rule, Rosas appointed José Seguí, among the few Afro Argentines to achieve a commissioned officer's rank, to administer Junín, in 1851. Seguí was an efficient, though repressive commander, and in 1863, he was assassinated at his nearby ranch.
Rosas' 1852 overthrow resulted in the appointment of a justice of the peace, who initially shared governing duties with the military commander.  Junín's first general store (Basterreix) opened in 1860, and in 1861, Junín elected its first city council (despite being officially only a fort). The province designated the area as a county in 1864, and with nearly 2,000 inhabitants, Junín ceases to be categorized as a "fort," and its first municipal master plan was laid out in 1865.
The 1880 arrival of the Central Argentine Railway and that of the Buenos Aires and Pacific Railway (B.A.& P.) in 1884 led to the town's rapid growth. The National Bank of Argentina had opened a branch there in 1892 and by the 1895 census, Junín was home to over 12,000. The town largest employer by then was the B.A.& P.'s rail equipment factory, which employed over 1,600. The City Hall was completed in 1904 and Junín was declared a "city," in 1906.
Junín's steady development over the subsequent decades and setting amid lakes made it a well-known regional tourist destination. A hunting club was established in 1938, and a fishermen's pier and club on Lake El Carpicho, in 1942.  The Aero Club Junín (1940) became well-known following the IX International Gliding Competition, in 1963, and the nearby Borchex Municipal Park and Lake Gómez both have become popular weekend destinations since the 1960s; Lake Gómez attracted around 350,000 visitors during the 2006-07 summer season. Nearby Estancia La Oriental has attracted growing rural tourism to the area, as well.
The city is home to an important Municipal Historical Museum, probably best known for its paleontology hall and its wooly mammoth fossils, and the Ángel María de Rosa Municipal Museum of Art (1944). In a bid to further diversify the city's economy, an industrial park was authorized north of the city in 1995, and a racetrack, the Autódromo Eusebio Marcilla, was opened in 2003. The closure of much of Argentina's passenger rail service during the 1990s was partly offset in Junín in part by the purchase of local rail facilities by América Latina Logística, a São Paulo-based rail transport provider operating largely in Argentina, as well as by establishment of the Junín Railworks Cooperative.
The city features numerous cinemas, as well as prominent stage theatres such as the Teatro de la Ranchería (1971). The city's first institution of higher learning, the Junín Regional University (CURJ), was established in 1990; fused with its 
Junín, Buenos Aires