Millwall Dock is a dock at Millwall, London, England, located south of Canary Wharf on the Isle of Dogs.
The Millwall Dock was constructed by John Aird & Co. to a design by Sir John Fowler and opened in 1868.
The dock is L-shaped, with an 'Outer Dock' running east-west, and an 'Inner Dock' running north from the eastern end. It originally contained around 36 acres (14 hectares) of water and had a 200-acre (81 hectare) estate. The western end of the Outer Dock was originally connected to the Thames at Millwall by an 80 ft (24 m) wide channel. The spoil from the docks formed the area of wasteland known as the Mudchute. A graving dock for ship repairs was constructed at the SE corner of the Outer Dock (one of 6 originally planned), and later lengthened to 555 ft (169 m).
With reorganisation by the Port of London Authority in the 1920s, the northern end of the Inner Dock was connected to the West India Docks by the Millwall Passage, and the direct connection to the Thames was filled.
The dock was used mainly for timber and grain, a trade which eventually moved down river to the Port of Tilbury with the construction of a major grain terminal in the 1960s. A McDougall's flour mill, the Wheatsheaf Mill (constructed in 1869), stood on the south side of the Outer Dock, but was demolished in about 1980. Nearby Sir John McDougall Gardens is named after one of the McDougall brothers, John McDougall, who was also a prominent local politician in Poplar.
Millwall Dock lies near the centre of the Isle of Dogs, just south of the now developed Canary Wharf commercial business area.