In order to talk about the origin of this district one has to go back to 1580 when Fernando Arias de Saavedra organizes an overland expedition from Asuncion, Paraguay arriving in Tandil, in the Province of Buenos Aires. He was accompanied by evangelized Guarani Indians who gave the area the name of TUYU and so, the Spaniards called it “Rincon del Tuyu”. The Jesuits and Franciscans and their missions provided the first geographical references of the area.
In the year 1744 Father Tomas Falkner takes charge of making a first topographical chart of the area and the Indians who served him as guides for their knowledge of the region give the area the name of AJO. The Ajo estuary became important as shelter for trading ships and also as place where produce coming from other parts of the country was gathered.
In the year 1825, Governor Juan Manuel de Rosas with his topographer, Senillosa include this area in the urbanization project of Dolores and Monsalvo, later resulting this last one in Ajo.
In 1870, the port of General Lavalle which was the only one in the area was at the highest point of the salting/curing of the leather industry, but it decays soon after the arrival of the first packing houses. As a result, the rural population decreases, those who stayed were employed by the Government for making roads and others found employment in Big Estates.
The “Partido de General Lavalle” was created 19 October 1891 and the borders of it begun at the “Rincon del Ajo”.
Starting in the year 1930, tourism is introduced in the area, and, as a result of this new communities are created such as San Clemente del Tuyu and Mar de Ajo. With the passing of the years, other local communities emerge like San Bernardo del Tuyu, Santa Teresita, Mar del Tuyu, Las Toninas, Costa Chica, Lucila del Mar, Costa Azul, Costa del Esta, Aguas Verdes, Nueva Atlantis, Pinar del Sol and Costa Esmeralda.
Creation of the Urban Municipalities: As these communities experience rapid growth with the influence of tourism, the Provincial Government passes Law 9024, 11 June 1978 and creates the “Urban Municipalities” which constitute the urban municipalities: De La Costa, Pinamar, Villa Gesell and Monte Hermoso. They officially become municipalities 23 May 1983 and form their first elected governments 30 October 1983 turning the “Urban Municipality of the Coast” into the “Partido de la Costa”.