1661 (MDCLXI) was a common year starting on Saturday of the Gregorian calendar and a common year starting on Tuesday of the Julian calendar, the 1661st year of the Common Era (CE) and Anno Domini (AD) designations, the 661st year of the 2nd millennium, the 61st year of the 17th century, and the 2nd year of the 1660s decade. As of the start of 1661, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.

• January 6 – The fifth monarchy men unsuccessfully attempt to seize control of London. George Monck's regiment defeats them.
• January 30 – The body of Oliver Cromwell is subjected to a posthumous execution.
• February 5 – The Shunzhi Emperor of the Qing Dynasty of China dies and is succeeded by his son the Kangxi Emperor.
• February 14 – George Monck’s regiment becomes The Lord General's Regiment of Foot Guards (which later becomes Coldstream Guards)
• April 23 – King Charles II of England, Scotland, Ireland crowned in Westminster Abbey. This is his second crowning.
• April 28 – The University of Santo Tomas in Manila opens. It is Asia's first University.
• June 30 – The first Earl of Argyle is executed at the Mercat Cross in Edinburgh for treason.
• August 6 – Portugal and the Dutch Republic sign the treaty of The Hague, whereby New Holland in present-day Brazil is ceded to Portugal.
• December 30 – Drottningholm Castle in Stockholm is destroyed by fire.

• Dutch rule ends in Taiwan.
• First modern bank notes issued in Stockholm, Sweden

• January 30 – Charles Rollin, French historian (d. 1741)
• March 25 – Paul de Rapin, French historian (d. 1725)
• April 16 – Charles Montagu, 1st Earl of Halifax, English poet and statesman (d. 1715)
• May 25 – Claude de Buffier, French philosopher and historian (d. 1737)
• June 6 – Giacomo Antonio Perti, Italian composer (d. 1756)
• June 9 – Tsar Feodor III of Russia (d. 1682)
• July 20 – Pierre Le Moyne, French founder of the Louisiana colony (d. 1706)
• September 2 – Georg Boehm, German organist (d. 1733)
• October 11 – Melchior de Polignac, French diplomat (d. 1742)
• November 1 – Florent Carton Dancourt, French dramatist and actor (d. 1725)
• November 4 – Karl Philip, Elector Palatine (d. 1742)
• November 6 – King Charles II of Spain (d. 1700)
• November 15 – Christoph Graffenried, Swiss settler in America (d. 1743)
• November 28 – Edward Hyde, 3rd Earl of Clarendon, Governor of New York and New Jersey (d. 1723)
• December 5 – Robert Harley, 1st Earl of Oxford and Mortimer, English statesman (d. 1724)
• December 18 – Christopher Polhem, Swedish scientist and inventor (d. 1751)

• January 19 – Thomas Venner, Fifth Monarchist
• February 2 – Lucas Holstenius, German humanist (b. 1596)
• February 5 – Shunzhi Emperor of China (b. 1638)
• March 1 – Richard Zouch, English jurist (b. 1590)
• March 9 – Cardinal Mazarin, French cardinal and statesman (b. 1602)
• April 4 – Alexander Leslie, 1st Earl of Leven, Scottish soldier (b. 1580)
• April 7 – William Brereton, English soldier and politician (b. 1604)
• May 27 – Archibald Campbell, 1st Marquess of Argyll, Scottish dissenter (b. 1607)
• August 7 – Jin Shengtan, Chinese editor, writer and critic (b. 1608)
• August 16 – Thomas Fuller, English churchman and historian (b. 1608)
• August 29 – Louis Couperin, French composer and organist (b. 1626)
• September 11 – Jan Fyt, Flemish painter (b. 1611)
• October 4 – Jacqueline Pascal, French child prodigy and sister of Blaise Pascal (b. 1625)
• October 28 – Agustin Moreto y Cavana, Spanish playwright (b. 1618)
• November 19 – Brian Walton, English clergyman and scholar (b. 1600)
• December 29 – Antoine Gerard de Saint-Amant, French poet (b. 1594)