Piedras Negras Municipality is a ane o the 38 municipalities o Coahuila, in northeastren Mexico. The municipal seat lees at Piedras Negras. The municipality covers an aurie o 914.2 km² an is locatit on the internaitional border atween Mexico an the USA, here formit bi the Río Bravo del Norte (Rio Grande), adjacent tae the U.S. state o Texas.