Coahuila, formally Coahuila de Zaragoza, officially Free and Sovereign State of Coahuila de Zaragoza, is one of the 31 states which, along with the Federal District, compose the 32 Federal Entities of Mexico. The state is located in Northeastern Mexico on the US border.
Coahuila borders the Mexican states of Nuevo León to the east, Zacatecas and San Luis Potosí to the south, and Durango and Chihuahua to the west. To the north, Coahuila accounts for a stretch of the Mexico-United States border, adjacent to the U.S. state of Texas along the course of the Rio Grande (Río Bravo del Norte). With an area of , it is the nation's third-largest state. It comprises 38 municipalities (municipios). In 2010, Coahuila's population is 2,748,391 inhabitants.
The Spanish explored the north of Mexico some decades after their victory in the capital of the Aztecs. Such exploration was delayed because the northern climate was harsher and there was no gold. The first Spanish settlement in the region now called Coahuila was at Minas de la Trinidad in 1577. Saltillo was settled in 1586 to form part of the province of New Spain, Nueva Vizcaya of the vice-royalty. Later it became one of the first provinces of Nueva Extremadura to be explored by Europeans.
"Coahuila and Texas" was one of the constituent states of the newly independent United Mexican States under its 1824 Constitution, and included Texas, Coahuila, and Nuevo León. Later in the same year Nuevo León was detached, but Texas remained a part of the state until 1835, when it seceded to form the Republic of Texas. Monclova was the capital of the state from 1833 to 1835.
In 1840 Coahuila briefly became a member of the short lived Republic of the Rio Grande.
On April 4, 2004, the border city of Piedras Negras was flooded. More than 30 people died and more than 4000 lost their homes. In 2007 Coahuila became the first state in Mexico to offer civil unions (Pacto Civil de Solidaridad) to same-sex couples.