Editing 1866 (section)

=== January–June ===
* January (date unknown) – [[Thomas Baldwin Marsh]], American religious leader (b. [[1799]])
* [[January 16]] – [[Phineas Quimby]], American physician (b. [[1802]])
* [[January 19]] – [[Harriet Ludlow Clarke]], British artist
* [[January 23]] – [[Thomas Love Peacock]], English satirist (b. [[1785]])
* [[January 31]] – [[Friedrich Rückert]], German poet, translator and professor of Oriental languages (b. [[1788]])
* [[February 25]] – [[Sarah Ann Gill]], Barbadian national heroine (b. [[1795]])
* [[March 4]] – [[Alexander Campbell (clergyman)|Alexander Campbell]], Irish/U.S. founder of the [[Disciples of Christ]] (b. [[1788]])
* [[March 6]] – [[William Whewell]], English scientist, philosopher and historian of science (b. [[1794]])
* [[March 20]] – [[Rikard Nordraak]], Norwegian composer (b. [[1842]])
* [[March 21]] – [[Nadezhda Durova]], first female Russian military officer (b. [[1783]])
* [[March 24]] – [[Maria Amalia of Naples and Sicily]], Queen of France (b. [[1782]])<ref>{{cite web |title=Marie-Amélie de Bourbon {{!}} queen of France {{!}} Britannica |url=https://www.britannica.com/biography/Marie-Amelie-de-Bourbon |website=www.britannica.com |access-date=6 September 2022 |language=en}}</ref>
* [[March 28]] – [[Solomon Foot]], American politician (b. [[1802]])
* [[March 29]] – [[John Keble]], British churchman (b. [[1792]])
* [[April 1]] – [[Elizabeth Jesser Reid]], English social reformer, founder of [[Bedford College (London)|Bedford College]] (b. [[1789]])
* [[April 4]]  – [[William Dick (veterinarian)|William Dick]], founder of [[Royal (Dick) School of Veterinary Studies|Edinburgh Veterinary College]] (b. [[1793]])
* [[April 5]] – [[Thomas Hodgkin]], British physician (b. [[1798]])
* [[April 7]] – [[Johann Sedlatzek]], German flautist (b. [[1789]])
* [[April 12]] – [[Peter Hesketh-Fleetwood]], English Member of Parliament and developer (b. [[1801]])
* [[May 13]] – [[Nikolai Brashman]], Russian mathematician of Czech origin (b. [[1796]])
* [[May 29]] – [[Winfield Scott]], American general and presidential candidate (b. [[1786]])
* [[June 7]] – [[Chief Sealth]], Native American for whom [[Seattle]] is named (b. c. [[1786]])
* [[June 17]] – [[Lewis Cass]], American military officer, politician, and statesman (b. [[1782]])