The village of El Castillo eventually grew around the fortress, which continued to be strategically important to the Captaincy General of Guatemala until the late 18th century.

The administrative capital of the municipality of El Castillo is the village of Boca de Sábalos, which translates from Spanish to "mouth of the tarpon" (Megalops atlanticus).

The municipality of El Castillo began with the construction of the Fortress of the Immaculate Conception on the southern bank of the San Juan River, approximately 6 kilometers from the present-day border with Costa Rica.

On the morning of July 26, 1762, a combined British and Miskito force laid siege to the fortress in what would later be called the Battle for the Río San Juan de Nicaragua.

[5] In 1781, King Charles III of Spain issued a royal decree granting Rafaela Herrera a pension for life, as a reward for her heroic defense during that battle.

[8] After Spain entered the American Revolutionary War in 1779, Major General John Dalling, the British governor and commander-in-chief of Jamaica, proposed a second naval expedition to Nicaragua.

The goal was to sail up the San Juan River to Lake Nicaragua and capture the town of Granada, which would effectively cut Spanish America in half as well as provide potential access to the Pacific Ocean.

[9] The 22-year-old Nelson, in command of HMS Hinchinbrook, was responsible for leading his men through dense jungle to attack the fortress from a hill in the rear.

This is largely due to the great distances between home and school facilities, lack of roads and suitable vehicles, and the difficult economic situations of many families of the community.