The town is divided into six districts: Ciutat Cooperativa-Molí Nou, Marianao-Can Paulet, Barri Centre, Vinyets-Molí Vell, Camps Blancs-Canons-Orioles, and Casablanca.
It is bordered on the north by the towns of Santa Coloma de Cervelló and Sant Joan Despí and the village of Sant Climent de Llobregat; on the east by the town of Cornellà de Llobregat; on the west by Viladecans; and on the south by El Prat de Llobregat and the Mediterranean Sea (via a narrow southward salient).
The finding of archaeological remains corresponding to Iberian colonies (VI-I bC) and to the Romans (I-V aC)―a noteworthy Roman bath is located near the river―suggests that Sant Boi was created in pre-Roman times.
As with most of the surrounding lands, from the 8th to the 11th century the town was controlled by the Moors, until their expulsion from Iberia during the Reconquista. The Moors called it Alcalá, which means “castle”, due to the existence of a hillock from where the river and the valley were dominated. The town’s current name is derived from the name of Saint Baudilus, known as Boi or Baldiri in Catalonia.
During the Middle Ages, the village progressively grew, expanding from the castle’s surroundings to adjacent zones. A baroque-style church was built during the 16th century. The growth continued in the following centuries, giving rise to numerous “masies” (typical Catalan agricultural country houses) near the river and fertile lands. By the end of the 19th century, Sant Boi was a village of nearly 5,000 inhabitants, with an economy driven mainly by agriculture.
In the early stages of the 20th century, industry arrived and subsequently flourished in Sant Boi, ranging from brick manufacturing to metalwork. With the end of the Spanish Civil War in 1939, there was a massive influx of immigrants from many different parts of Spain. These new arrivals consisted mostly of people from villages and small towns. They were searching for jobs and career opportunities in the city of Barcelona since it was stimulated by the regrowth of Catalan industry in post-war Spain.
The population rose from 10,000 people in 1940 to 65,000 in 1975. This period is characterized by the construction of complete quarters (Casablanca, Camps Blancs, and Cooperativa) for the housing of immigrants. Sant Boi is now a town with more than 80,000 inhabitants, with well-established industrial and service sectors, and good cultural and recreational offerings.