Noticed by Ferdinand Magellan in 1520, who gave nearby Cape San Antonio its name, Spanish authorities first surveyed the area in 1580.

A fishing wharf became Ajó's economic hub in subsequent decades, and had been prominent as a supply route during the 1838 French blockade against Rosas.

The installation of abattoirs (since closed) was followed by new fishermen's docks, a canal, a Buenos Aires Great Southern Railway terminal, and two lighthouses built between 1878 and 1902.

During the last dictatorship, the military-appointed Governor, General Ibérico Saint Jean, signed Decree 9024, the Urban Jurisdictions Law of June 11, 1978, by which the Lavalle District was divided into three (the others being Pinamar and Villa Gesell).

The economic malaise Argentina suffered in the 1980s and the boom in overseas travel following recovery in the early 1990s took its toll on municipal finances, however.