Year 1742 (MDCCXLII) was a common year starting on Monday (link will display the full calendar) of the Gregorian calendar and a common year starting on Friday of the 11-day slower Julian calendar.
January - June
July - December
- Daniel le Pelley succeeds Nicolas le Pelley as Seigneur of Sark.
- The Kingdom of Prussia captures Jihlava.
- Christian Goldbach formulates Goldbach's conjecture.
- Colin Maclaurin publishes his Treatise on Fluxions.
- Anders Celsius proposes the Celsius temperature scale (see 1741).
- James Bradley succeeds Edmond Halley as Astronomer Royal.
- Henry Fielding publishes Joseph Andrews.
- John Carteret, 2nd Lord Carteret becomes Secretary of State for the Northern Department in Great Britain.
- The rigging of the Chippenham by-election causes a political scandal in Great Britain.
- William Pulteney is created as 1st Earl of Bath in Great Britain.
- Robert Walpole is elevated to the peerage and thus moves from the House of Commons of Great Britain to the House of Lords, effectively ending his reign as Prime Minister of Great Britain (see February 16, above).
- The University of Erlangen is founded.
- The Lopukhina Conspiracy arises at the Russian court.
- Molde, Norway becomes a city.
- Construction starts on the Foundling Hospital in London.
- Eisenach, Germany builds its Stadtschloss (city castle).
- In Peru, Juan Santos takes the name Atahualpa II and begins an ill-fated rebellion against the Spanish rule.
- The Afghan tribes unite as a monarchy.
- Charles Jervas's English translation of Don Quixote is published posthumously. Through a printer's error, the translator's name is printed as Charles Jarvis, leading the book to forever be known as the Jarvis translation. It is acclaimed as the most faithful English rendering of the novel made up to that time.
- Spain completes the construction of Fort Matanzas in the Matanzas Inlet, approximately 15miles south of St. Augustine, Florida.
- Rome decrees that Roman ceremonial practice in Latin (not in Chinese) is to be the law for Chinese missions.
- January 8 - Philip Astley, English circus organizer (d. 1814)
- February 28 - Steven Banik, Renaissance man (d. 1744)
- March 10 - Sampson Salter Blowers, American lawyer and jurist (d. 1842)
- April 28 - Henry Dundas, British statesman (d. 1811)
- May 6 - Jean Senebier, Swiss pastor and botanist (d. 1809)
- June 25 - Johann Schweighauser, German classical scholar (d. 1830)
- June 26 - Arthur Middleton, American politician (d. 1787)
- June 28 - William Hooper, American statesman (d. 1790)
- July 21 - John Cleves Symmes, American statesman (d. 1814)
- July 27 - Nathanael Greene, American general (d. 1786)
- September 14 - James Wilson, American politician (d. 1798)
- October 6 - Johan Herman Wessel, Norwegian poet (d. 1785)
- December 9 - Carl Wilhelm Scheele, Swedish chemist (d. 1785)
- December 16 - Gebhard Leberecht von Blücher, Prussian general (d. 1819)
- date unknown
- probable - Joseph Brant, Mohawk leader (d. 1807)
- January 1 - Peregrine Bertie, 2nd Duke of Ancaster and Kesteven, English statesman (b. 1686)
- January 14 - Edmond Halley, English astronomer (b. 1656)
- February 22 - Charles Rivington, English publisher (b. 1688)
- March 23 - Jean-Baptiste Dubos, French author (b. 1670)
- April 2 - James Douglas, Scottish physician and anatomist (b. 1675)
- April 17 - Arvid Horn, Swedish statesman (b. 1664)
- May 13 - Ludwig IX, Landgrave of Hesse-Darmstadt (b. 1719)
- May 21 - Lars Roberg, Swedish physician (b. 1664)
- May 26 - Pylyp Orlyk, Ukrainian Zaporozhian Cossack starshina, diplomat (b. 1672)
- June 18 - John Aislabie, British politician (b. 1670)
- June 27 - Nathan Bailey, English philologist and lexicographer
- July 4 - Guido Grandi, Italian mathematician (b. 1671)
- July 9 - John Oldmixon, English historian (b. 1673)
- July 12 - Evaristo Abaco, Italian composer (b. 1675)
- July 14 - Richard Bentley, English scholar and critic (b. 1662)
- July 19 - William Somervile, English poet (b. 1675)
- August 25 - Carlos Seixas, Portuguese composer (b. 1704)
- September 22 - Frederic Louis Norden, Danish explorer (b. 1708)
- September 27 - Hugh Boulter, Irish Archbishop of Armagh (b. 1672)
- September 28 - Jean Baptiste Massillon, French bishop (b. 1663)
- November 12 - Friedrich Hoffmann, German physician and chemist (b. 1660)
- November 20 - Melchior de Polignac, French diplomat (b. 1661)
- November 24 - Andrew Bradford, American publisher (b. 1686)
- December 31 - Karl III Philip, Elector Palatine (b. 1661)