El Rosario belonged to the department of San Salvador until February 21, 1852, when the Department of La Paz was established and Zacatecoluca was named as the departmental headquarters whose administrative area was now to include the town of El Rosario while still a part of the Olocuilta district.

By Legislative Decree No 486, dated November 18, 1998, El Rosario obtained the title of city, under the administration of Julio Arevalo Diego Bonilla.

The administration of former President Dr. Armando Calderon Sol bestowed the title of City in a solemn public ceremony in the town's Central Park on December 19, 1998.

“Partido de Conciliación Nacional” (The Party of National Conciliation) and currently A.R.E.N.A “Alianza Republicana Nacionalista” (The Nationalist Republican Alliance).

is credited with modernizing the city of El Rosario by implementing the construction of concrete streets and a municipal soccer stadium.