Designed by the firm Robert Matthew Johnson-Marshall Partnership and built between 1969-77, the building became the home of Gwent County Council when it opened in 1974. The building was acquired by the newly created Monmouthshire County Council and Torfaen County Council in 1996 following the Local Government Act 1994 which reorganised the governing administrations of Wales. In March 2012 the building closed following a report which revealed repair costs would amount to £30m. A subsequent structural survey then showed the building had 'concrete cancer', with the steel reinforcements in the structure rusting due to water penetration. Monmouthshire Council offices temporarily moved to Magor before a permanent move to Usk in 2013, while Torfaen is largely based at Pontypool civic centre. The old county hall at Cwmbran was finally demolished in 2013 and the site sold to Kier Group for residential development.

Meilyr Powel, RCAHMW, October 2020.

Sources:

'Cwmbran County Hall demolition may need hole filling', BBC News, 27 October 2012
John Newman, The Buildings of Wales: Gwent/Monmouthshire (Penguin Books, UWP, 2000), p.79
'Old Gwent County Council headquarters site in Croesyceiliog to get almost 150 new homes', South Wales Argus, 20 August 2019

The mid 20th century saw prolonged discussion amoung Monmouthshire County Council about a building to replace the 19th century County Hall in Newport. In 1951 three sites were assessed as part of the development of Cwmbran New Town, in conjunction with the Cwmbran New Town Development Corporation. A site at Croesyceiliog, one of the western suburbs of the town, was considered most suitable. Because this lay just outside the Designated Area, a 'county hall Sites committee' instead looked at a compulsory purchase order of land at llanfrechfa in 1952, though by 1955 had returned to discussions with the CDC about the Croesyceiliog site. In 1962, with the run-up to new legislation leading to the creation of gwent as one of the new 13 counties of Wales, Monmouthshire county council were again assessing a number of sites. Work on the new county hall at Croesyceiliog finally started in 1969, designs provided by the private practise of Robert Matthew, Johnson-Marshall and Partners. the complex accommodated 500 staff, 88 council members and parking for 200. 

The complex was an architecturally striking example, probably the best example, of the new batch of county halls built as part of the 1974 county realignment. The Y-plan buildngs has horizontal bands of bronzed glass windows alternated with bands of dark aggregate panels, while a series of terraces created open walkways to the council chamber block. Demolished in 2013, the site has since lain unused. 

S Fielding July 2021

Cwmbran New Town: A urban Characterisation (RCAHMW, 2021)