Guayanilla is a town and municipality of Puerto Rico located on the 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 barrios and Guayanilla Pueblo. It is part of the Yauco Metropolitan Statistical Area.

The municipalities of Puerto Rico are the second-level administrative divisions in the Commonwealth of Puerto Rico. There are 78 such administrative divisions covering all 78 incorporated towns and cities. Each municipality is led by a mayor and divided into barrios, third-level administrative divisions, though the latter are not vested with any political authority. Every municipality is governed as stated by the Autonomous Municipalities Act of 1991, which establishes that every municipality must have an elected strong mayor with a municipal legislature as the form of government. Each legislature must be unicameral, with the number of members related to adequate representation of the total population of the municipality. In contrast to other jurisdictions, both the mayors and the municipal legislators are elected on the same date and for the same term of four years in office.