The municipality of El Oro is one of the 39 Municipalities of Durango, in northwestern Mexico. The municipal seat is in Santa María del Oro. The municipality has an area of 3,559.0 km². As of 2010, the municipality had a total population of 11,320, starting with 10,041 as of 2005. The municipality had 113 locations, the largest of which was: Santa María del Oro.