| Official Name: | Monacillo |
| Native Name Lang: | es |
| Settlement Type: | Barrio |
| Coordinates Footnotes: | [1] |
| Subdivision Type: | Commonwealth |
| Subdivision Name: |  Puerto Rico |
| Subdivision Type1: | Municipality |
| Subdivision Name1: | San Juan |
| Unit Pref: | Imperial |
| Area Total Sq Mi: | 1.15 |
| Area Land Sq Mi: | 1.15 |
| Area Water Sq Mi: | 0 |
| Population As Of: | 2010 |
| Population Note: | 2010 census |
| Population Total: | 11442 |
| Population Density Sq Mi: | 9949.6 |
| Timezone: | AST |
| Utc Offset: | -4 |
| Elevation Ft: | 246 |
| Postal Code Type: | ZIP Code |
See main article: San Juan, Puerto Rico.
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 km2). 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.[2]