The Onon (Mongolian: Онон гол, Onon gol; Russian: Оно́н) is a river in Mongolia and Russia. It is 818 km long and drains an area of 94,010 km2. It originates at the eastern slope of the Khentii Mountains. For 298 km it flows within Mongolia. It joins with Ingoda River to produce the Shilka River.
|Nickname(s)||Queen Mother Onon|
|Native name||Онон гол|
|⁃ location||eastern Khentii Mountains|
|Length||817 km (508 mi)|
|Basin size||94,010 km2 (36,300 sq mi)|
The Onon—Shilka—Amur water system is one of the world's ten longest rivers, measuring 818 km + 560 km + 2,874 km.
The upper Onon is one of the areas that are claimed to be the place where Genghis Khan was born and grew up.
The Secret History of the Mongols begins thus: "There came into the world a "Borte Chono" (blue-gray wolf) whose destiny was Heaven’s will. His wife was a "Gua Maral" (beautiful fallow doe). They traveled across the inland sea and when they were camped near the source of the Onon River in sight of Burkhan Khaldun, their first son was born, named Bat Tsagaan."