| 138961 | December 9 | Event | 1962 – The Petrified Forest National Park is established in Arizona. |
| 138962 | December 9 | Event | 1965 – Kecksburg UFO incident: A fireball is seen from Michigan to Pennsylvania witnesses report something crashing in the woods near Pittsburgh. In 2005 NASA admits that it examined the object. |
| 138963 | December 9 | Event | 1965 – A Charlie Brown Christmas, first in a series of Peanuts television specials, debuts on CBS. |
| 138964 | December 9 | Event | 1966 – Barbados joins the United Nations. |
| 138965 | December 9 | Event | 1968 – Douglas Engelbart gave what became known as "The Mother of All Demos", publicly debuting the computer mouse, hypertext, and the bit-mapped graphical user interface using the oN-Line System (NLS). |
| 138966 | December 9 | Event | 1969 – U.S. Secretary of State William P. Rogers proposes his plan for a ceasefire in the War of Attrition Egypt and Jordan accept it over the objections of the PLO, which leads to civil war in Jordan in September 1970. |
| 138967 | December 9 | Event | 1971 – The United Arab Emirates join the United Nations. |
| 138968 | December 9 | Event | 1971 – Indo-Pakistani War: The Indian Air Force executes an airdrop of Indian Army units, bypassing Pakistani defences. |
| 138969 | December 9 | Event | 1973 – British and Irish authorities sign the Sunningdale Agreement in an attempt to establish a power-sharing Northern Ireland Executive and a cross-border Council of Ireland. |
| 138970 | December 9 | Event | 1979 – The eradication of the smallpox virus is certified, making smallpox the first and to date only human disease driven to extinction. |
| 138971 | December 9 | Event | 1987 – Israeli–Palestinian conflict: The First Intifada begins in the Gaza Strip and West Bank. |
| 138972 | December 9 | Event | 1988 – The Michael Hughes Bridge in Sligo, Ireland, is officially opened. |
| 138973 | December 9 | Event | 2003 – A blast in the center of Moscow kills six people and wounds several more. |
| 138974 | December 9 | Event | 2008 – The Governor of Illinois, Rod Blagojevich, is arrested by federal officials for crimes including attempting to sell the U.S. Senate seat being vacated by President-elect Barack Obama's election to the Presidency. |
| 138975 | December 9 | Event | 2013 – At least seven are dead and 63 are injured following a train accident near Bintaro, Indonesia. |
| 138976 | December 9 | Birth | 1447 – Chenghua Emperor of China (d. 1487) |
| 138977 | December 9 | Birth | 1508 – Gemma Frisius, Dutch mathematician and cartographer (d. 1555) |
| 138978 | December 9 | Birth | 1561 – Edwin Sandys, English politician (d. 1629) |
| 138979 | December 9 | Birth | 1571 – Metius, Dutch mathematician and astronomer (d. 1635) |
| 138980 | December 9 | Birth | 1579 – Martin de Porres, Peruvian saint (d. 1639) |
| 138981 | December 9 | Birth | 1594 – Gustavus Adolphus of Sweden (d. 1632) |
| 138982 | December 9 | Birth | 1608 – John Milton, English poet and philosopher (d. 1674) |
| 138983 | December 9 | Birth | 1610 – Baldassare Ferri, Italian singer and actor (d. 1680) |
| 138984 | December 9 | Birth | 1652 – Augustus Quirinus Rivinus, German physician and botanist (d. 1723) |
| 138985 | December 9 | Birth | 1667 – William Whiston, English mathematician, historian, and theologian (d. 1752) |
| 138986 | December 9 | Birth | 1717 – Johann Joachim Winckelmann, German archaeologist and historian (d. 1768) |
| 138987 | December 9 | Birth | 1721 – Peter Pelham, English-American organist and composer (d. 1805) |
| 138988 | December 9 | Birth | 1728 – Pietro Alessandro Guglielmi, Italian composer (d. 1804) |
| 138989 | December 9 | Birth | 1745 – Maddalena Laura Sirmen, Italian violinist and composer (d. 1818) |
| 138990 | December 9 | Birth | 1748 – Claude Louis Berthollet, French chemist and academic (d. 1822) |