Guayanilla (Spanish pronunciation: [ɡwaʝaˈniʎa]) is a municipality of Puerto Rico located in southern coast of the island, bordering the Caribbean Sea, south of Adjuntas, east of Yauco; and west of Peñuelas and about 12 miles (19 km) west of Ponce. Guayanilla is spread over 16 wards and Guayanilla Pueblo (the downtown area and the administrative center of the city). It is part of the Yauco Metropolitan Statistical Area.
Guayanilla was founded by Puerto Rican criollos. The original name was Guadianilla in memory of a river of the same name in Spain. However, it was changed to Guayanilla to resemble a native word in the Taíno dialect. The name Guayanilla is derived from a combination of Guaynia and Santa Maria de Guadianilla.
The first Europeans settled in this area in 1511. In 1756, Yauco was founded as a town. Then Guayanilla was a borough of Yauco.