Chongming, formerly known as Chungming, is an alluvial island at the mouth of the Yangtze River in eastern China covering 1,267 square kilometers as of 2010. Together with the islands Changxing and Hengsha, it forms Chongming County, the northernmost area of the provincial-level municipality of Shanghai. Following its massive expansion in the 20th century from sediment deposited by the Yangtze, Chongming is now the 2nd-largest island administered by the People's Republic of China.