The island was discovered on December 3, 1460 and named Llana until salt deposits were found at the end of the 18th century in Pedra de Lume. In the early years, slaves grazed parts of the island, in the 17th century, free settlers took salt. Sal is the geologically oldest island in Cape Verde, formed 50 million years ago during the eruption of a volcano which is now inactive.
Salt activity did not begin until 1800. Sal at the time was the least populated island in Cape Verde, and once had around the same population as Santa Luzia. Santa Maria was founded on the south of the island in 1835 by Manuel António Martins who became governor and had the town become the island's capital. 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. Three lighthouses were constructed near the island's hazardous points in the 1880s.
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. Planes from Italy would stop to briefly refuel before continuing their flights to various South American cities. Northeast of the airport, workers from São Nicolau Island to the west would settle a village and was named Preguiça, where the first settlers originated and the youngest urban center in Cape Verde, Palmeira was later founded and became the island's other port, not long after it became Espargos due to the asparagus plants founded there and became the main island capital as well as a commercial center, a part of the population growth was and still is attributed to arrivals from São Nicolau.
Unlike other parts of Cape Verde, famine did not devastate the island as the population was only about 500 in 1930 and it was one of few islands up to 1970 that saw its population continue to grow. Farmlands were established around 2 km northwest of Espargos in the mid 20th century. A new solar electricity station was established in 2010 and is located 1.5 km north of Santa Maria on the main road, the first and only in Cape Verde. A large growing population has now led to the division of the municipality, of which the first plan was proposed on April 7, 2014, no date of the separation has yet been set. It would form the municipalities of Espargos and Santa Maria, the municipal boundary would be marked north of Ilhéu Rabe de Junco, north of Murdeira and south of the airport, probably in the east-west line, also Nossa Senhora das Dores will exclude Santa Maria.
Hurricane Fred struck the island of Sal in late summer 2015, the hardest was on August 31, in Santa Maria, where the storm surge sunk or stranded dozens of vessels and destroyed an important tourist pier. Hotels, restaurants, and other beach facilities were flooded, and roads in the town became impassable. High winds leveled the roof of a sport center at a gymnasium which had initially been set up as a storm shelter to about 100 citizens. Elsewhere, the hurricane knocked out power to homes in Palmeira and caused minor structural damage to Sal International Airport.
The island is 35 km long and about 12 km wide. It is one of the three sandy eastern islands (Sal, Boa Vista and Maio) of the archipelago, with white sandy beaches. The island is fairly flat, with the highest elevation being 408 m at Monte Grande. Serra Negra has a height of 92 m.
Sal is one of five islands that have one or more surrounding islets, the largest being Ilhéu Rabo de Junco.
In recent years, trees started to appear in the smallest parts of the island, as of 2015, trees became dominant in most of the dry streams and within riverbeds. In the south, trees are founded particularly in resort areas. The north and the northeast remains not to be forested.
Sal Island has on average 350 days of sunshine a year. Winds mainly blow from the northeast. However, some days do also have clouds, but they tend to be scattered and seldom bring rain. The 'rainy season' is from July to mid-October, although rainfall is still low.
Saline marshes can be found in the Pedra de Lume crater and north of Santa Maria.
As of 1832, the population was estimated at 400 people. The population reached 1,000 around the early 20th century, making it the least populated island of the nine inhabited islands at the time. The population started growing at a steady pace, and in 1950 and 1960 the population more than doubled. Until 1970 the population rose more than 10% a year to 5,505. After 1970 its growth remained moderate. In 1990 another large population growth occurred which brought the population to nearly 15,000 at the end of the 20th century, and in 2010, the population reached 35,000. With population growth came the urban sprawl which creeped to east of Espargos and to the northern and western parts of Santa Maria along with hotels and villas which first began developing in 2006. The island population is now currently around 40,000 and is now the fifth most populated island in Cape Verde. In 1990, it surpassed Brava's population, and in 2000, it surpassed the neighboring São Nicolau's population.
Sal’s main town, Cidade dos Espargos, is home to one of the nation’s international airports and has around 32,000  inhabitants. Its population grew around salt collection and later shifted to fishing, but is now based on tourism (amounting to 50% of the archipelago’s tourism) at the beach resort of Santa Maria. The living standards on the island is among the best in the Cape Verde archipelago. The island's GDP per capita as of July 2015 is roughly $7,068.00(USD).
Its airport, Amílcar Cabral International Airport, was used as a refuelling base by South African Airways on its Johannesburg to London routes. This was necessitated by the refusal of Black African states to the North to grant overflying permission and direct routing to and from Europe during apartheid. Later, flights to and from New York and Atlanta also refuelled there, and the island was a crew-change station. SAA established the long runways needed by the fully fueled Boeing 747s on their take-offs in the high temperatures. On July 1, 2006, SAA operated its final flight to Sal due to the ending of its flights to Atlanta.
The major roads on the island are:
There are six inhabited centers:
Other inhabited settlements are:
Football (soccer) is the chief sports on the island. It has the Sal Regional Football Association and its main competitions are the Premier and the Second Divisions. Its main clubs are Académica do Sal, Académico do Aeroporto, Juventude and SC Santa Maria. The island's main stadium is Estádio Marcelo Leitão situated southeast of Espargos's center and all regional matches are played. Also Basketball is the second most popular on the island as well as volleyball, they are played at Polidesportivo do Sal, Académico do Sal is the island's best basketball team. Futsal is also played. Also dominant particularly in the beaches the south of the island and its surrounding waters are surfing, windsurfing and kitesurfing, recently gained for about 25 years and becoming the most dominant in the nation in windsurfing and kitesurfing.
Sal is twinned with: