Editing 1821 (section)

=== July–December ===
[[File:John William Polidori by F.G. Gainsford.jpg|thumb|right|110px|[[John William Polidori]]]]
* [[July 4]] – [[Richard Cosway]], English artist (b. 1742)
* [[July 14]] – [[Pedro Juan Caballero (politician)|Pedro Juan Caballero]], Paraguayan captain (b. 1786) (suicide)
* [[July 17]] – [[Fulgencio Yegros]], Paraguayan general and politician (b. 1780)
* [[August 7]] – [[Caroline of Brunswick]], Queen of the United Kingdom (b. 1768)
* [[August 20]] – [[Dorothea von Medem]], Latvian diploma, duchess of Courland (b. 1761)
* [[August 24]] – [[John William Polidori]], English physician, writer (b. 1795) (suicide)<ref>{{Cite journal|last=Viets|first=Henry R.|date=1961|title="By The Visitation Of God": The Death Of John William Polidori, M.D., In 1821|journal=The British Medical Journal|volume=2|issue=5269|pages=1773–1775|doi=10.1136/bmj.2.5269.1773|jstor=20356143|pmid=14037964|pmc=1970869|issn=0007-1447}}</ref>
* [[September 4]] – [[José Miguel Carrera]], Chilean general, founding father (b. 1785)
* [[September 10]] – [[Johann Dominicus Fiorillo]], German painter, art historian (b. 1748)
* [[September 14]] – [[Heinrich Kuhl]], German naturalist, zoologist (b. 1797)
* [[October 4]] – [[Marie-Louise Lachapelle]], French [[obstetrician]] (b. 1769)
* [[October 6]] – [[Anders Jahan Retzius]], Swedish chemist, botanist (b. 1742)
* [[October 8]] – [[Juan O'Donojú]], viceroy of New Spain (b. 1762)
* [[October 11]] – [[John Ross Key]], American judge, lawyer, father of songwriter [[Francis Scott Key]] (b. 1754)
* [[October 21]] – [[Dorothea Ackermann]], German actress (b. 1752)
* [[November 8]] – [[Jean Rapp]], French general (b. 1771)
* [[December 4]] – [[John Henniker-Major, 2nd Baron Henniker]], British politician (b. 1752)
* [[December 7]] – King [[Pōmare II]] of Tahiti (b. 1782)
* [[December 12]] – [[Phoebe Hessel]], British female soldier (b. 1713)