Baja California Sur (lit. "South Lower California"), officially Free and Sovereign State of Baja California Sur, is the smallest Mexican state by population and the 31st admitted state of the 31 states which, with the Federal District, make up the 32 Federal Entities of Mexico. Before becoming a state on October 8, 1974, the area was known as the South Territory of Baja California. It has an area of , or 3.57% of the land mass of Mexico and occupies the southern half of the Baja California peninsula, south of the 28th parallel. It is bordered to the north by the state of Baja California, to the west by the Pacific Ocean, and to the east by the Gulf of California, also known as the "Sea of Cortés." Also, the state has maritime borders with Sonora and Sinaloa to the east across the Gulf of California.
As of 2010, the population was 637,026. The state is home to the tourist resorts of Cabo San Lucas and San José del Cabo. Its largest city and capital is La Paz, a tourist resort and historic landmark. It includes Loreto, the historic first capital of all three Californias (Baja California Sur, Baja California, and California), the town of Santa Rosalía which is the site of a historic church designed by Gustave Eiffel.
The first inhabitants are thought to have arrived to the peninsula at least 11,000 years ago, to judge by the archaeological discovery of several Clovis points in the northern part of the state. The possibility of an even earlier occupation has been raised by radiocarbon dates from a site on Isla Espíritu Santo, but this interpretation still remains controversial.
Before phases of the state's prehistory are manifested in several archaeological complexes:
Four distinct ethnolinguistic groups were encountered in Baja California Sur by the early explorers and missionaries: the Pericú in the south, between Cabo San Lucas and La Paz, and on several of the islands in the Gulf; the Guaycura from La Paz to south of Loreto; the Monqui, in the area around Loreto; and the Cochimí, in extensive areas throughout the middle of the peninsula.
The European discovery of Baja California Sur is credited to Fortún Ximénez, a mutineer on an expedition dispatched by the conqueror of central Mexico, Hernán Cortés in early 1533. Cortés himself led an expedition to the "Island of California" 1535, but he soon abandoned the fruitless enterprise. In 1539–1542, both coasts of Baja California Sur were reconnoitered by Francisco de Ulloa and Juan Rodríguez Cabrillo. Over the next century and a half, a variety of explorers and pearl hunters (including Sebastián Vizcaíno) visited the peninsula's shores but seem to have had little lasting impact.
The Jesuits began their involvement in 1683–1685 when Eusebio Francisco Kino, along with the admiral Isidro de Atondo y Antillón, made two major but ultimately unsuccessful efforts at colonization, at La Paz and then at San Bruno, north of Loreto. In 1697 the Jesuit missionary Juan María de Salvatierra established Misión de Nuestra Señora de Loreto Conchó, the first permanent mission in Baja California Sur. Jesuit control over the peninsula was gradually extended, first in the region around Loreto, then to the south in the Cape region, and finally toward the north across the northern boundary of Baja California Sur.
The Jesuits were expelled from the peninsula in 1768 and replaced by the Franciscans under Junípero Serra. In 1773, the Franciscans in turn ceded control of the Baja California missions to the Dominicans. The native population of Baja California Sur steadily diminished during the colonial period, primarily under the impacts of Old World diseases but also in occasional violent conflicts. While the Jesuits had striven to limit lay Spanish or Mexican settlement on the peninsula, fearful of corrupting influences and competing power centers, the missions under the Franciscans and Dominicans had to accept a growing lay presence and increased control from central New Spain.
The peninsula was divided into two separate entities in 1804, with the southern one having the seat of government established in the port of Loreto.
After the Mexican War of Independence, President Guadalupe Victoria named Lt. Col. José María Echeandía governor of Baja California Sur and divided it in four municipios (municipalities). In 1830, the capital was moved to La Paz after Loreto was partially destroyed by heavy rains.
On October 2, 1847 the army of the United States was defeated near the town of Mulegé by Captain Manuel Pineda, as part of the Mexican-American War. As a consequence of this battle, the U.S. army was forced to withdraw from the peninsula and could not lay claim to it as part of the new territories acquired through the Treaty of Guadalupe Hidalgo of 1848.
In 1853, a group of 45, led by journalist William Walker, without the authorization of the United States Government, captured the city of La Paz, before the Mexican Army forced the 45 to retreat back to the United States.
The Territory of Baja California was created in 1888 under the government of President Porfirio Díaz. In 1930, Baja California was again divided into North and South parties, renamed later as North and South districts, then, into North and South territories.
In 1952, the North Territory of Baja California became the 29th state of Mexico, Baja California. The southern portion, below 28°N, remained a federally administered territory until 1974, when the South Territory of Baja California became the 31st state, Baja California Sur, along with the state of Quintana Roo.