To the north, Coahuila accounts for a stretch of the U.S. - Mexico border, adjacent to the U.S. state of Texas along the course of the Rio Grande (Río Bravo del Norte). Coahuila also borders the Mexican states of Nuevo León to the east, Zacatecas and San Luis Potosi to the south, and Durango and Chihuahua to the west. With an area of , it is the nation's third-largest state. It comprises 38 municipalities (municipios). In 2005, Coahuila's population was 2,495,200 inhabitants. Coahuila's population is comprised mainly of people of European ancestry, making up 74 per cent of the population. The second-largest ethnic group is the Mestizo (European-Amerindian) who are 20 per cent of the population, and the smallest ethnic group is the Amerindian, comprising 1 per cent of Coahuila's population. The rest of the population is composed of American, Canadian, and Japanese communities.
The capital of Coahuila and its largest city is Saltillo. Coahuila also includes the cities of Torreón (the largest metropolitan area of the state but part of this metro area is in the neighboring state of Durango), Monclova (a former state capital), Piedras Negras, and Ciudad Acuña.
East of the range, the land slopes gently toward the Rio Grande, and is drained by several rivers, including the Salado and its tributary the Sabinas. The Tamaulipan mezquital, a dry shrubland ecoregion, occupies the western portion of the state, and extends across the Rio Grande into southern Texas.
The portion of the state west of the Sierra Madre Oriental lies on the Mexican Plateau, and is part of the Chihuahuan Desert. The Bolsón de Mapimí is a large endorheic basin which covers much of the western portion of the state and extends into adjacent portions of Chihuahua, Durango, and Zacatecas. The Nazas River, which flows east from Durango, and the Aguanaval River, which flows north from Zacatecas, empty into lakes in the Bolsón. Torreón, the most populous city in the state, lies on the Nazas in the irrigated Laguna Region, the (Comarca Lagunera), which straddles the border of Coahuila and Durango.
The state contains two biosphere reserves. Maderas del Carmen lies on the northern border of the state, and includes sections of the Chihuahuan desert and sky islands of pine-oak forest in the Sierra del Carmen. The springs, lakes, and wetlands of Cuatro Ciénegas lie west of Monclova on the west slope of the Sierra Madre.
The state is largely arid or semi-arid, but the rivers of the state support extensive irrigated agriculture, particularly cotton. The Parras district in the southern part of the state produces wines and brandies. The pine-oak forests of the Sierra Madre produce timber.
Coahuila y Tejas ("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 Leon. Later in the same year Nuevo Leon 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.
In 2007, Coahuila became the first state in Mexico to offer civil unions (Pacto Civil de Solidaridad) to same-sex couples.
As of 2005, Coahuila’s economy represents 3.5% of Mexico’s total gross domestic product or 22,874 million USD. Coahuila's economy has a strong focus on export oriented manufacturing (i.e. maquiladora / INMEX). As of 2005, 221,273 people are employed in the manufacturing sector. Foreign direct investment in Coahuila was 143.1 million USD for 2005. The average wage for an employee in Coahuila is approximately 190 pesos per day.