The island was discovered on December 3, 1460 and named Llana (“flat”). This name was changed into the current “Sal” when the two large salt ponds (Pedra de Lume and Santa Maria) were discovered.
The first three centuries after its discovery, the island was only sparsely inhabited; in 1720 there was a small fishing village near present Palmeira.
This changed when the salt industry was developed at the end of the 18th century, starting in Pedra de Lume. Santa Maria was founded in the south of the island in 1830 by Manuel António Martins.
During this time the salt industry thrived, with 30,000 tons of salt being exported in the early years. Most of the salt was exported to Brazil until its nationalization in 1887, Portuguese and French salt investors resumed salt production until 1984.
In 1939 Italy started constructing an airport to receive flights from Europe and South America. Construction was halted and ceased around World War II. The Portuguese bought the airport from the Italians and finished it in 1949. Northeast of the airport, workers from São Nicolau Island settled in a village named Preguiça, now part of Espargos.