Monacillo is one of the 18 barrios in the municipality of San Juan, Puerto Rico. The barrio included the area that now forms Monacillo Urbano. In 2010, it had a population of 11,442 living in a land area of 1.15 square miles (2.98 km<sup>2</sup>). Monacillo is surrounded by Monacillo Urbano barrio to the north, Cupey to the east, Caimito to the south, and the municipality of Guaynabo to the west.