Placentia is the name of some places in the world:

• Placentia, Newfoundland and Labrador, Canada
• Placentia, California, United States of America
• The Palace of Placentia was a royal palace in Greenwich, London
• Piacenza in Italy was formerly called Placentia in Latin and English
• Placencia de las Armas and Plentzia are in the Basque Autonomous Community, Spain.