Dated 1922 and officially opened on Monday 21 January 1924, Twyn County Junior School is a late example of the Baroque revival style. It was designed by D Pugh Jones, Glamorgan County Architect, who designed several schools in Caerphilly. From the inscriptions above the doors it appears that girls occupied the ground floor, using the side entrances, whilst boys occupied the 1st floor, accessed from the front.

There are four ranges around a central courtyard, The front faces North and contains a central block which is higher and projects slightly. Built from coursed rock-faced stone with sandstone dressings, it has quoin strips, sill bands, impost bands and lintels. It also has a slate roof with wide modillion eaves. There is a segmental arched opening into the basement storey with a large keystone, above which is a tablet bearing a shield and the inscription 'Glamorgan County Council, 1922'.

It is listed as an inter-war school of considerable architectural character, the plan form and the Baroque style detail being exceptional for this period.

Sources:- Cadw listed buildings, NJR 18/03/2009; 'Caerphilly's New School', Western Mail, 18 January 1924, p.11