Los Fresnos (the ashes) gets its name from the Ash trees in the area is at the intersection of State Highway 100 and Farm Road 1847, ten miles north of Brownsville in south central Cameron County.
According to local history a ranch by that name was established in the area as early as 1770. The land on which the town is situated, however, was part of the El Portero del Espíritu Santo (also known as El Agostadero del Espíritu Santo) land grant, issued by Spain to José Salvador de la Garza in 1781. He established a ranch on the land he received and called it Rancho El Espíritu Santo. Garza and other local residents conducted open-range grazing, especially of sheep, until after the Mexican War.