* 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 – Italy and Prussia ally against the Austrian Empire.

* 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

* Civil Rights Act of 1866, extending the rights of emancipated slaves by stating that any person born in the United States regardless of race is a U. S. citizen.

* 1866 – Reconstruction: Tennessee becomes the first U. S. state to be readmitted to the Union following the American Civil War.

Both the Imperial and U. S. definitions of the nautical mile were based on the Clarke ( 1866 ) Spheroid: they were different approximations to the length of one minute of arc along a great circle of a sphere having the same surface area as the Clarke Spheroid.

Furthermore, Davis accused Gould of having misrepresented a study by Henry H. Goddard ( 1866 – 1957 ) about the intelligence of Jewish, Hungarian, Italian, and Russian immigrants to the U. S., wherein Gould reported Goddard's qualifying those people as " feeble-minded "; whereas, in the initial sentence of the study, Goddard said the study subjects were atypical members of their ethnic groups, who had been selected because of their suspected sub-normal intelligence.

The Civil Rights Act of 1866 had already granted U. S. citizenship to all persons born in the United States, as long as those persons were not subject to a foreign power ; the framers of the Fourteenth Amendment added this principle into the Constitution to prevent the Supreme Court from ruling the Civil Rights Act of 1866 to be unconstitutional for lack of congressional authority to enact such a law and to prevent a future Congress from altering it by a mere majority vote.

* Treaty of Washington ( 1866 ), between the U. S. and the Potawatomi

It was moved to Washington, D. C. in 1866, colocating with the U. S. Naval Observatory in 1893.

* George Edmund Badger ( 1795 – 1866 ), U. S. Senator from North Carolina

Founded as the Missouri Dental College in 1866, the Washington University School of Dental Medicine was the first dental school west of the Mississippi River and the sixth dental school in the U. S. The school closed in 1991.

Accounts differ as to the county's namesake: either Thomas Harlan, or James Harlan, who was U. S. Secretary of the Interior between 1865 and 1866.

A U. S. post office was established at Hibernia on June 19, 1849, but its name was changed on October 17, 1853 to Magnolia Mills, and on July 30, 1866, it was changed to Green Cove Springs.

When Grant Township was organized in 1866, it was named for then General ( and later U. S. President ) Ulysses S Grant.

* Robert S. Hale, U. S. Representative from New York, December 3, 1866 to March 3, 1867 and March 4, 1873 to March 3, 1875

In Ex parte Garland, 71 U. S. 333 ( 1866 ), the court struck down a federal law requiring attorneys practicing in federal court to swear that they had not supported the rebellion.

He was mustered out of the volunteer service on September 1, 1866, and retired from the U. S. Army on October 15, 1868, with the regular army rank of major general.

* Henry Cantwell Wallace ( 1866 – 1924 ), U. S. Secretary of Agriculture, father of Henry A. Wallace

It was the first U. S. soft drink, originating in 1866, although it was modelled on imported Irish ginger beers.

On July 17, 1866, President Andrew Johnson nominated Porter for appointment as brevet brigadier general, to rank from March 13, 1866, and the U. S. Senate confirmed the appointment on July 23, 1866.

The Army's presence, U. S. political pressure, and the growing resistance of Benito Juárez induced the French to abandon their claims against Mexico and Napoleon III withdrew his troops in 1866.

Cave Johnson ( January 11, 1793 – November 23, 1866 ) was for fourteen years a Democratic U. S. Congressman from Tennessee.

On April 14, 1866, one year to the day after Abraham Lincoln's assassination, the U. S. Post Office issued its first postage stamp honoring the fallen President.