* Herbert Austin ( 1866 – 1941 ), British founder of the Austin Motor Company

* 1866 – The Grand Army of the Republic, an American patriotic organization composed of Union veterans of the American Civil War, is founded.

* 1866 – Felix-Raymond-Marie Rouleau, Canadian cardinal of the Roman Catholic Church ( d. 1931 )

* 1866 – Princess Viktoria of Prussia ( d. 1929 )

* 1866 – Allen Lard, American golfer ( death date unknown )

* 1866 – Giovanni Agnelli, Italian businessman, founded Fiat S. p. A ( d. 1945 )

* 1866 – Gábor Klauzál, Hungarian politician ( b. 1804 )

* 1866 – Matthew Henson, American explorer ( d. 1955 )

* 1866 – José de Diego, Puerto Rican statesman and journalist ( d. 1918 )

* 1866 – Charles Jean de la Vallée-Poussin, Belgian mathematician ( d. 1962 )

* 1866 – Italo Santelli, Italian fencer ( d. 1945 )

* 1866 – Jacinto Benavente, Spanish writer, Nobel Prize laureate ( d. 1954 )

* 1866 – Henrik Sillem, Dutch sports shooter ( d. 1907 )

* Alexander John Cuza, prince of Romania ( 1859 – 1866 )

* 1866 – Austro-Prussian War ends with the Treaty of Prague.

* 1866 – Anne Sullivan, American teacher, instructor and companion of Helen Keller ( d. 1936 )

* 1866 – Ernest Starling, British physiologist ( d. 1927 )

* 1866 – The American Society for the Prevention of Cruelty to Animals ( ASPCA ) is founded in New York City by Henry Bergh.

He married fourthly at the Dolmabahçe Palace, Constantinople, on 21 September 1866 to Georgian HH Hayranidil Kadın Efendi ( Kars, 2 November 1846 – Ortaköy Palace, Constantinople, 26 November 1898 ), and had two children.

The Earl of Derby, Prime Minister 1852, 1858 – 59, 1866 – 68

Charles Erdman ( 1866 – 1960 ) advocated apostolic authorship and wrote that only the Apostle John fits the image of the author derived from the text.

#** Marie Laetitia Eugénie Catherine Adélaïde Bonaparte ( 1866 – 1926 )

Le déjeuner sur l ' herbe, ( right section ), with Gustave Courbet, 1865 – 1866, Musée d ' Orsay, Paris, France | Paris

Politics surrounding the 1866 war against Austria allowed Italy to annex Venetia, which had been a kingdom of the Austrian Empire since the 1815 Congress of Vienna.

* 1866 – Venice-Annexion of Veneto and Mantua to Italy-At Hotel Europa, Austria hands over Veneto to France, which hands it immediately over to Italy.

* 1866 – A plebiscite ratifies the annexion of Veneto and Mantua to Italy, occurred three days before, on October 19.

In 1866, following the Third Italian War of Independence, Venice, along with the rest of the Veneto, became part of the newly created Kingdom of Italy.

In 1866 Venetia was ceded by France, who had obtained it from Austria at the end of the Austro-Prussian War, to the new Kingdom of Italy, which had been created in 1861 under the Savoy monarchy.

The Republic wasn't restored at the Congress of Vienna after the Napoleonic Wars and was annexed by the Austrian Empire, until it was ceded to the Kingdom of Italy in 1866, as a result of the Third Italian War of Independence.

Thus, Veneto would remain under Austrian rule, except for some cities which declared their independence in 1848, until it was annexed by the Kingdom of Italy in 1866.

In 1866, after the Third War of Independence and a controversial referendum, Veneto was annexed to Italy.

In 1866, Mantua was incorporated in the united Italy by the king of Sardinia.

In 1866 the battle of Koniggratz gave Italy the opportunity, as an allied of Prussia, to take Venetia, and Padua was as well annexed to the recently formed Kingdom of Italy.

Annexed to Italy during 1866, Padua was at the centre of the poorest area of Northern Italy, as Veneto was until 1960s.

One of the main figures of the unification of Italy, Giuseppe Mazzini, was elected deputy at Messina in the general elections of 1866.

In 1866 he fought under Giuseppe Garibaldi in the Seven Weeks War in which the Kingdom of Italy and Prussia fought against Austria, after which Venice was ceded to Italy.

The villages of Breginj, Logje, Sedlo, Kobarid, Borjana, Robidišče, Homec, Stanovišče, Podbela, Livek and Livške Ravne in the municipality of Kobarid are also part of the historical region of Venetian Slovenia ; they were however not annexed to the Kingdom of Italy in 1866, and are now part of the Republic of Slovenia.

In 1866, the region became part of Italy by a referendum, with the exception of the villages of Breginj and Livek which were included in the Austrian County of Gorizia and Gradisca.

Venice was subjected first to French rule, then to Austrian, and finally in 1866 it became part of Italy.

The Third Independence War was declared by the new Kingdom of Italy against the Austrian Empire, in 1866, with the alliance of the Kingdom of Prussia.

In 1866 Italy signed alliance with Prussia against Austria.

Lombardy was annexed to Sardinia in 1859, and Venetia to the new kingdom of Italy in 1866, at which point the Lombardy-Venetia stamps went out of use.

The first fleet action between ironclad ships was fought in 1866 at the Battle of Lissa between the navies of Austria and Italy.

After the short French domination which ensued, it was part of the Austrian-puppet Lombardy-Venetia Kingdom, and was included in the newly formed Kingdom of Italy in 1866.