1721 in architecture

The year 1721 in architecture involved some significant events.

• Bocking Windmill, Essex, England.
• 7 Burlington Gardens, later Queensberry House, London, Giacomo Leoni's first design for England
• Fort King George, along the Altamaha River in the modern-day US state of Georgia
• Ruthven Barracks in Scotland completed
• Jackson Square (New Orleans), New France
• Nazarbaug Palace, Gujarat, India
• Ellingen Residence in Ellingen, Bavaria completed in its Baroque form
• Písek Gate, Prague, Czech Republic
• Saint Paul the First Hermit Cathedral completed as parish church of San Pablo, Laguna, Philippines

• Grand Prix de Rome, architecture: Philippe Buache.

• March 5 – John Adam, architect, brother of Robert Adam and James Adam (died 1792)
• March 26 - Nicolas Le Camus de Mézières, French architect (Bourse de Commerce) and author (died 1793)
• date unknown
  • Francesco Sabatini, Sicilian architect working in Spain (died 1797)
  • Thomas Sandby, English draughtsman, watercolour artist, architect, and teacher (died 1798)

• February 11 – Carlo Francesco Bizzaccheri, Italian architect (born 1656)
• June 11 – Sir Anthony Deane, English naval architect, shipbuilder and politician (born 1633)