|Covid-19|February – France, Savoy, and Venice sign the Treaty of Paris, agreeing to cooperate in removing Spanish forces from the strategic Alpine pass of Valtelline.
February 25 – Thirty Years' War: Duke Maximilian I of Bavaria becomes Elector of the Electorate of the Palatinate.
March 5 – The first American temperance law is enacted, in Virginia.
March 9 – Amboyna massacre: Ten men in the service of the British East India Company, nine Japanese and one Portuguese, are executed by the Dutch East India Company.
March 20 – Richard Frethorne begins writing a letter to his parents from Jamestown, Virginia.
April 11 – King Gwanghaegun of Joseon is deposed in a coup. He is succeeded by King Injo.
April 29 – A fleet of 11 Dutch ships depart for the coast of Peru, seeking to seize Spanish treasure.
June 14 – The first breach-of-promise lawsuit: Rev. Gerville Pooley, in Virginia, files against Cicely Jordan, but loses.
June 29 – Première of Pedro Calderón de la Barca's first play, Amor, honor y poder, at the Court of Habsburg Spain.
July – The ship Anne arrives from England at "New Plymouth" (Plymouth Colony), carrying more settlers, followed a week or two later by the Little James.
Papal Conclave of 1623: Pope Urban VIII (Maffeo Barberini) succeeds Pope Gregory XV as the 235th pope.
Thirty Years' War: Chased by the Count of Tilly's army, Christian of Brunswick's army attempts to flee to the Dutch Republic. Tilly's army catches Brunswick five miles from the border. In the resulting Battle of Stadtlohn, Christian's army is destroyed.
September 10 – Murat IV (1623–1640) succeeds Mustafa I (1622–1623) as Ottoman Emperor.
November 1 – Fire at Plymouth Colony destroys several buildings.
Between November 8 and early November – Publication in London of the "First Folio" (Mr. William Shakespeares Comedies, Histories, & Tragedies), a collection of 36 of the plays of Shakespeare, half of which have not previously been printed.
The Safavids recapture Baghdad.
England first colonizes Saint Kitts and Nevis.
Wilhelm Schickard invents his "Calculating Clock", an early mechanical calculator.
Zildjian begins the commercial manufacture of cymbals in Turkey. The company will still be operating, from Massachusetts, in the 21st century.
Procopius' long-lost Secret History is rediscovered in the Vatican Library.
Giambattista Marini publishes his long poem Adone.
Tommaso Campanella publishes The City of the Sun.
Johannes Rudbeck founds Rudbeckianska gymnasiet, the first gymnasium in Sweden.
The second Thanksgiving is celebrated at Plymouth Plantation.
Erotomania is first mentioned in a psychiatric treatise.
On the coast of Massachusetts Bay, the settlement that will become the City of Gloucester, Massachusetts is first inhabited by men from Dorchester, England.
On the coast of New Hampshire, the settlement of Hilton's Point that will become Dover is established by men from London, England, the first European settlers in the state.
January 1 – Marie Eleonore of Dietrichstein, German noblewoman by birth member of the House of Dietrichstein and by her two marriage Countess of Kaunitz and Oppersdorf (d. 1687)
January 15 – Algernon Sidney, British philosopher (d. 1683)
February 2 – David Questiers, Dutch poet (d. 1663)
March 4 – Jacob van der Does, Dutch landscape painter (d. 1673)
March 5 – Henri Sauval, French historian (d. 1676)
March 23 – Deane Winthrop, Sixth son of Governor John Winthrop (d. 1704)
March 24 – Ralph Hare, English politician (d. 1672)
April 7 – Thomas Mainwaring, English politician (d. 1689)
April 11 – Decio Azzolino, Italian Catholic Cardinal (d. 1689)
April 20 – Olimpia Aldobrandini, Aldobrandini family member (d. 1681)
April 23 – Sir John Chichester, 1st Baronet, English politician (d. 1667)
April 27 – Gryzelda Konstancja Zamoyska, Polish noble (d. 1672)
April 28 – Wilhelmus Beekman, Dutch politician (d. 1707)
April 30 – François de Laval, first Roman Catholic bishop of Quebec (d. 1708)
May 26 – William Petty (d. 1687)
May 27 – Sir William Petty, English scientist and philosopher (d. 1687)
May 29 – David Schirmer, German lyric poet and librarian (d. 1686)
John Egerton, 2nd Earl of Bridgewater, English politician (d. 1686)
Wallerant Vaillant, painter of the Dutch Golden Age (d. 1677)
June 8 – Paluzzo Paluzzi Altieri degli Albertoni, Italian Catholic Cardinal (d. 1698)
June 15 – Cornelis de Witt, Dutch politician (d. 1672)
June 19 – Blaise Pascal, French mathematician, physicist, and philosopher (d. 1662)
June 29 – Inaba Masanori, Daimyo (d. 1696)
July 1 – William Owfield, English landowner and politician (d. 1664)
July 6 – Jacopo Melani, Italian composer and violinist (d. 1676)
July 12 – Elizabeth Walker, English pharmacist (d. 1690)
July 28 – Allen Brodrick, English politician (d. 1680)
August 4 – Friedrich Casimir, Count of Hanau-Lichtenberg (1641–1680) and Hanau-Münzenberg (1642–1680) (d. 1685)
August 5 – (baptism) Antonio Cesti, Italian composer (d. 1669)
August 13 – Sir John Morden, 1st Baronet, English politician (d. 1708)
August 14 – Sir John Fowell, 2nd Baronet, English politician (d. 1677)
August 23 – Stanisław Lubieniecki, Polish Socinian theologist (d. 1675)
August 25 – Filippo Lauri, Italian painter (d. 1694)
August 26 – Johann Sigismund Elsholtz, German naturalist and physician (d. 1688)
September 1 – Caspar Schamberger, German surgeon and merchant (d. 1706)
September 8 – James Bellingham, English politician (d. 1650)
September 10 – Carpoforo Tencalla, Swiss-Italian Baroque painter of canvases and frescoes (d. 1685)
September 13 – Pieter Wouwerman, Dutch painter (d. 1682)
September 21 – Sir John Bowyer, 1st Baronet, English soldier and politician (d. 1666)
September 23 – Georg Balthasar Metzger, German physician and scientist (d. 1687)
October 4 – Robert Thoroton, English antiquary (d. 1678)
October 9 – Ferdinand Verbiest, Flemish Jesuit missionary in China during the Qing dynasty (d. 1688)
October 17 – Francis Turretin, Swiss-Italian Reformed scholastic theologian (d. 1687)
October 28 – Johann Grueber, Austrian Jesuit missionary and astronomer in China (d. 1665)
November 1 – Zhu Youlang, Prince of Gui, the Yongli Emperor, the 4th and last emperor of the Southern Ming Dynasty of China (d. 1662)
November 5 – Mariana of the Purification, Nun of the Carmelite Order of the Ancient Observance (d. 1695)
November 17 – Philip Sherard, English politician (d. 1695)
November 22 – Bussy Mansell, Welsh Member of the Parliament of England (d. 1699)
November 28 – Giovanni Battista Caccioli, Italian painter (d. 1675)
December 1 – Christian Louis I, Duke of Mecklenburg-Schwerin (1658–1692) (d. 1692)
December 8 – Ernest, Landgrave of Hesse-Rheinfels and later of Hessen-Rheinfels-Rotenburg (d. 1693)
December 13 – Marc-René de Voyer de Paulmy d'Argenson, French politician and diplomat (d. 1700)
December 16 – Ercole, Marquis of Baux, member of the House of Grimaldi (d. 1651)
December 23 – Matthias Palbitzki, Swedish diplomat and art-connoisseur (d. 1677)
December 28 – Elisabeth Augusta Lindenov, daughter of king Christian IV of Denmark (d. 1677)
Margaret Cavendish, Duchess of Newcastle (d. 1673)
Francis Talbot, 11th Earl of Shrewsbury (d. 1667)
January 1 – Paul Hentzner, German lawyer and traveller in England during the late Elizabethan era (b. 1558)
January 11 – Pieter van Mierevelt, Dutch painter (b. 1596)
January 15 – Paolo Sarpi, theologian (b. 1552)
February – Malcolm Macfie, last chief of the Scottish clan Clan Macfie
February 8 – Thomas Cecil, 1st Earl of Exeter, English politician (b. 1546)
February 19 – Clara Maria of Pomerania-Barth, German noble (b. 1574)
March 7 – Luís Mendes de Vasconcellos, 55th Grandmaster of the Knights Hospitaller (b. c. 1542)
March 19 – Philip Sigismund of Brunswick-Wolfenbüttel, Roman Catholic bishop (b. 1568)
Henri de La Tour d'Auvergne, Duke of Bouillon (b. 1555)
Henri de La Tour d'Auvergne, vicomte de Turenne, duc de Bouillon (b. 1555)
March 29 – Scévole de Sainte-Marthe, French poet (b. 1536)
April 14 – John Scudamore, English politician (b. 1542)
April 19 – Uesugi Kagekatsu, Japanese samurai and warlord (b. 1556)
April 26 – Bálint Lépes, Hungarian cardinal (b. c. 1570)
May 1 – Matthew Clerke, English politician (b. 1564)
May 4 – Asprilio Pacelli, Italian Baroque composer (b. 1570)
May 19 – Mariam-uz-Zamani, Empress of the Mughal Empire (b. 1542)
May 23 – Edward Lawley, English politician (b. 1586)
May 26 – Francis Anthony, English apothecary and physician (b. 1550)
June 16 – Christian, Duke of Brunswick-Lüneburg-Wolfenbüttel, German Protestant military leader (b. 1599)
June 28 – Federico Ubaldo della Rovere, Duke of Urbino, Italian noble (b. 1605)
July 3 – Claes Michielsz Bontenbal, Dutch civil servant (b. 1575)
July 4 – William Byrd, English composer (b. 1543)
July 8 – Pope Gregory XV (b. 1554)
July 12 – William Bourchier, 3rd Earl of Bath (b. 1557)
August 6 – Anne Hathaway, wife of William Shakespeare (b. 1555)
August 9 – George, Count of Nassau-Dillenburg, Count of Nassau-Beilstein (1607–1620), then Count of Nassau-Dillenburg (1620–1623) (b. 1562)
August 12 – Stefano Pignatelli, Catholic cardinal (b. 1578)
August 18 – Samuel Sandys, English politician (b. 1560)
August 31 – Jacob van Wassenaer Duivenvoorde, Dutch admiral (b. 1574)
September 1 – Marcantonio Gozzadini, Catholic cardinal (b. 1574)
September 26 – Edwin Sandys, English politician (b. 1591)
September 27 – Johann VII, Count of Nassau-Siegen (b. 1561)
September 28 – Johann Georg, Prince of Hohenzollern-Hechingen (b. 1577)
October 21 – William Wade, English statesman and diplomat (b. 1546)
October 23 – Henry Curwen, English politician (b. 1581)
November 9 – William Camden, English antiquarian (b. 1551)
November 11 – Philippe de Mornay, French writer (b. 1549)
November 12 – Josaphat Kuncevyc, Lithuanian archbishop (b. c. 1582)
November 13 – Erdmuthe of Brandenburg, Duchess of Pomerania-Stettin (b. 1561)
December 4 – Jerome de Angelis, Italian jesuit missionary to Japan (b. 1567)
December 24 – Michiel Coignet, Flemish mathematician, astronomer, engineer, etc. (b. 1549)
date unknown – Andrea Andreani, Italian engraver (b. 1540)
1623 (MDCXXIII) was a common year starting on Sunday (dominical letter A) of the Gregorian calendar and a common year starting on Wednesday (dominical letter E) of the Julian calendar, the 1623rd year of the Common Era (CE) and Anno Domini (AD) designations, the 623rd year of the 2nd millennium, the 23rd year of the 17th century, and the 4th year of the 1620s decade. As of the start of 1623, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.