[3] The plan was for the west wing to contain a geological museum managed by the Royal Geological Society of Cornwall, the east wing was to contain the municipal offices, the courtrooms and a police station while the central section was to contain the main assembly hall known as St John's Hall, a name which was eventually adopted locally for the whole complex.

[4] Foundation stones for each of west, east and central wings of the new building were laid by Charles Fox, President of the Geological Society, the mayor of Penzance and the High Sheriff of Cornwall respectively on 27 April 1864.

[5][6] The complex was designed by John Matthews in the neoclassical style, built in ashlar stone from Lamorna Quarry by Olver & Sons of Falmouth and was officially opened on 10 September 1867.

[1] A concert organ, designed and manufactured by Henry Bryceson, was installed in the main assembly hall,[9] and the suffragette, Helen Beedy, give a speech in front of an audience of 600 people there in December 1874.

[16] Following the completion of an extensive programme of refurbishment works, which included the conversion of the west wing into a public library and the conversion of the east wing into modern offices for the use of Cornwall Council staff delivering local services,[17] the building was re-opened by the Duke and Duchess of Cornwall in July 2016.