The year 1805 in architecture involved some significant events.

• November 26 – The Ellesmere Canal's Pontcysyllte Aqueduct, designed by Thomas Telford and William Jessop, is opened on the border of Wales, the tallest and longest in Britain.^[1]
• Theatre Royal, Bath, England is opened.
• Evangelical Lutheran Church of Saint Mary in Saint Petersburg is built.
• Haga Palace in Stockholm, Sweden, designed by Carl Christoffer Gjörwell, is completed.

• Grand Prix de Rome, architecture: Auguste Guenepin

• March 11 – Thomas Ellis Owen, English architect working chiefly around Southsea (d. 1862)
• June 9 – Victor Baltard, French architect (d. 1874)
• July 26 – John Miller, Scottish railway civil engineer (d. 1883)
• Peter Ellis, English architect working in Liverpool (d. 1884)
• James Salmon, Scottish architect (d. 1888)

• Peter Atkinson, English architect (b. 1725)