Faced in Portland stone and an imposing example of 'Edwardian Baroque' style, construction of the main six storey building of County Hall begun in 1911. The architect Ralph Knott won the keenly contested commission to create a home for the London County Council, beating numerous well established architects to design the project at the young age of 29. Construction was delayed by the outset of the First World War, during which Knott worked on designs for Royal Air Force bases, and was officially opened by King George V in 1922. The later buildings comprising the North, South and Island blocks were completed later, the last being in 1974.

County Hall, also known as London County Hall, LCH, served as the headquarters of local government for London for over sixty years. The original London County Council was replaced by the Greater London Council, GLC, in 1965. During the 1980s the GLC was under the powerful control of the Labour Party and the front of the County Hall frequently served as a billboard for political slogans against the Conservative government led by Prime Minister Margaret Thatcher. The site was especially prominent for sloganeering uses due to the proximity of the parliament buildings across the river Thames. When the GLC was abolished by the conservatives in 1986, County Hall lost its role as the seat of government in London as power was devolved to the local London Boroughs.

Following dissolution of the GLC, talk soon centred around what was to happen to the building. Plans to relocate the Westminster campus of the London School of Economics f to the site were overruled by the government, perhaps due to the risk of further sloganeering from the students.

The County Hall is now the site of a variety of businesses and attractions. These include the Dali Universe and The London Aquarium. The visitor centre for the nearby London Eye is also situated inside the building.