Hengsha Island in the context of "Shanghainese"

Chongming (Chinese: 崇明岛), formerly romanized as Chungming, is an alluvial island at the mouth of the Yangtze River in East China covering 1,267 square kilometers (489 sq mi) as of 2010. Together with the islands Changxing and Hengsha, it forms Chongming District, the northernmost area of the provincial-level municipality of Shanghai. At the time of the 2010 Chinese census, its population was 660,000.

A 20-kilometer-long (12 mi) stretch of the north shore of the island is not part of Chongming District of Shanghai but are instead two pene-exclaves of Jiangsu, formed by the connection of Chongming to the formerly-separate island of Yonglongsha.

The islands of Shanghai are those under the jurisdiction of the Shanghai municipal government. They comprise three large inhabited islands and a shifting number of smaller, uninhabited ones. Most are alluvial islands in the Yangtze River Delta in China, although a number of islands in Hangzhou Bay off Jinshan District are also administered by Shanghai. The alluvial islands are relatively young and their number varies over time. In 2006, the city's 19 uninhabited islands covered 226.27 square kilometers (87.36 sq mi), with a total coastline length of 309 kilometers (192 mi).

The Yangshan area of the Port of Shanghai is also located on two islands, Greater and Lesser Yangshan in Hangzhou Bay, but these are administered as part of Zhejiang's Shengsi County.

Chongming District (pronunciation) is the northernmost district of the provincial-level municipality of Shanghai. Chongming consists of three low-lying inhabited alluvial islands at the mouth of the Yangtze north of the Shanghai peninsula: Chongming, Changxing, and Hengsha. Following its massive expansion in the 20th century, Chongming is now the 2nd-largest island administered by the People's Republic of China and the 3rd-largest in Greater China, after Hainan. Chongming does not, however, administer all of the island: owing to its continual expansion from sediment deposited by the Yangtze, it has merged with formerly separate islands and now includes Jiangsu province's pene-exclave townships of Haiyong and Qilong. Chongming proper covers an area of 1,411 km (545 sq mi) and had a population of 637,921 at the time of the Census 2020.

The county was established in 1396, the second year of the Ming dynasty's Hongwu Emperor. With the completion of the Yangtze and Chongqi Bridges, it is now connected to both the rest of Shanghai and southeastern Jiangsu province along the Hushan Expressway. Further development is now proceeding according to an urban and agricultural master-plan led by Philip Enquist of SOM, although ambitious plans for an ecocity named Dongtan have been shelved since the 2006 ouster of mayor Chen Liangyu and other neighborhoods have swelled with immigration from people relocated from central China following the completion of the Three Gorges Dam.