district, administrative and historic county of Cambridgeshire, east-central England, occupying an area northeast of the city of Cambridge. Situated predominantly within the Fens, an expanse of reclaimed marshland, the district has a slightly elevated chalk upland (which is covered by unstratified glacial drift) in the southeast.

Prior to the draining of the Fens in the 17th century, Ely was an isolated locale on an island of glacial drift amid the marshlands; today the town of Ely, with its famous cathedral, is the district seat. The section of the Fens around Ely is an important area for sugar beet cultivation; cereals, onions, potatoes, fruits, and various other horticultural produce are also intensively grown. Wicken Fen, 10 miles (16 km) south of Ely, is the only substantial remnant of undisturbed marshland in the Fens. A haunting place rising several feet above the adjacent cultivated lands, Wicken Fen's 730 acres (295 hectares) are a sanctuary for rare insects, birds, and plants. The mostly rural district has few woodlands and little industry. Littleport, Soham, and Haddenham are local agricultural centres in the Fens. The Stained Glass Museum in the cathedral at Ely displays panels of painted glass representing the development of the craft from the 14th century to the present. Area 253 square miles (656 square km). Pop. (2001) 73,216.