According to the 2002 census of the National Statistics Institute, Placilla spans an area of 146.9 km2 (57 sq mi) and has 8,078 inhabitants (4,134 men and 3,944 women). Of these, 2,114 (26.2%) lived in urban areas and 5,964 (73.8%) in rural areas. The population grew by 3.6% (279 persons) between the 1992 and 2002 censuses.
As a commune, Placilla is a third-level administrative division of Chile administered by a municipal council, headed by an alcalde who is directly elected every four years. The 2012–2016 mayor was José Joaquín Latorre Muñoz (PDC); Latorre, however, died as a consequence of a car crash on 22 July 2013. Latorre had previously held the mayoral office between 1992 and 2008. He was succeeded by Tulio Contreras Álvarez, a member of the local council.