At the end of the 18th century, Spanish Dominican missionaries and friars gave the name of El Rosario to an indigenous settlement in the area.

The town was part of the mission of San Miguel Arcangel de la Frontera, located a few miles to the south.

The mission was founded on March 28, 1787 by the Dominican friar Luis Sales on the banks of the San Juan Bautista stream.

After the Mexican–American War and the Treaty of Guadalupe Hidalgo, the new Mexican border lay no more than 30 km (18.5 miles) from Rosarito.

[7] Other than the city of Playas de Rosarito, the municipality had 358 localities, the largest of which (with 2010 populations in parentheses) were: Ampliación Ejido Plan Libertador (5,906), Primo Tapia (4,921), classified as urban, and Ciudad Morelos (2,040), Colinas del Sol (1,361), and Santa Anita (1,284), classified as rural.