The main six storey building was designed by Ralph Knott.
It is faced in Portland stone in an Edwardian Baroque style.
 The construction, which was undertaken by Holland, Hannen & Cubitts, started in 1911 and the building was opened in 1922 by King George V.  The North and South blocks, which were built by Higgs and Hill, were added between 1936 and 1939.
The Island block was not completed until 1974.

For 64 years County Hall served as the headquarters of local government for London.
During the 1980s the then powerful Labour-controlled GLC led by Ken Livingstone was locked in conflict with the Conservative national government of Margaret Thatcher.
Since the Parliament buildings were just across the river from County Hall, the façade of County Hall frequently in more than one year of her tenure served as a billboard for opposition slogans.
When the government of Margaret Thatcher abolished the GLC in 1986, County Hall lost its role as the seat of London's government.
Talk soon became of what was to happen to the building, and plans to relocate the London School of Economics to the site from its Westminster campus were overruled by Thatcher, seemingly disapproving of further slogans from students.
The building remained in use by the Inner London Education Authority (ILEA) until its abolition in 1990 when the building was transferred to the London Residuary Body and eventually sold to private investors.

On 21 October 2005, the High Court of England and Wales upheld a bid by the owners of the building, Shirayama Shokusan, to have the Saatchi Gallery evicted on grounds of violating its contract, particularly using space outside of the rented area for exhibits.

The County Hall Island Block, an annex of the main building, was demolished in 2006 to make way for a hotel, the Park Plaza Westminster Bridge.
The building, also known as No 1 Westminster Bridge Road, had been disused since 1986 and had become a derelict eyesore.

A blue plaque commemorates the LCC, GLC and the Inner London Education Authority at County Hall.
The main six storey building was designed by Ralph Knott. It is faced in Portland stone in an Edwardian Baroque style.  The construction, which was undertaken by Holland, Hannen & Cubitts, started in 1911 and the building was opened in 1922 by King George V.  The North and South blocks, which were built by Higgs and Hill, were added between 1936 and 1939. The Island block was not completed until 1974.
For 64 years County Hall served as the headquarters of local government for London. During the 1980s the then powerful Labour-controlled GLC led by Ken Livingstone was locked in conflict with the Conservative national government of Margaret Thatcher. Since the Parliament buildings were just across the river from County Hall, the façade of County Hall frequently in more than one year of her tenure served as a billboard for opposition slogans. When the government of Margaret Thatcher abolished the GLC in 1986, County Hall lost its role as the seat of London's government. Talk soon became of what was to happen to the building, and plans to relocate the London School of Economics to the site from its Westminster campus were overruled by Thatcher, seemingly disapproving of further slogans from students. The building remained in use by the Inner London Education Authority (ILEA) until its abolition in 1990 when the building was transferred to the London Residuary Body and eventually sold to private investors.
On 21 October 2005, the High Court of England and Wales upheld a bid by the owners of the building, Shirayama Shokusan, to have the Saatchi Gallery evicted on grounds of violating its contract, particularly using space outside of the rented area for exhibits.
The County Hall Island Block, an annex of the main building, was demolished in 2006 to make way for a hotel, the Park Plaza Westminster Bridge. The building, also known as No 1 Westminster Bridge Road, had been disused since 1986 and had become a derelict eyesore.
A blue plaque commemorates the LCC, GLC and the Inner London Education Authority at County Hall.
County Hall, London