Mid Glamorgan was formed in 1974 under the Local Government Act 1972. It consisted of part of the former administrative county of Glamorgan, and the county borough of Merthyr Tydfil, along with the parishes of along with the parishes of Penderyn and Vaynor from Breconshire (or Brecknockshire) and the urban districts of Bedwas and Machen, Rhymney and part of Bedwellty, from Monmouthshire.
It was divided into six districts:
Mid Glamorgan and its component districts were abolished in 1996 and the area split into the unitary authorities of Bridgend, Merthyr Tydfil, Rhondda Cynon Taf and part of Caerphilly as a result of the Local Government (Wales) Act 1994.
The communities of Wick, St. Bride's Major, Ewenny (from the Ogwr district) became part of the Vale of Glamorgan county borough, while Pentyrch (from the Taff-Ely district) was added to the Cardiff unitary authority area. Because of this, they became part of the preserved county of South Glamorgan. In 2003 the ceremonial borders were further adjusted, placing the entire Caerphilly county borough in the ceremonial county of Gwent.
The county council's offices were located in the Glamorgan Building (the former headquarters of Glamorgan County Council), in Cathays Park, Cardiff, in effect, outside of the Mid Glamorgan boundaries.
The county council's coat of arms was very similar to that of the previous council of Glamorganshire:
The crest, as with Glamorganshire, was the same Welsh dragon rising from flames, only this time supporting a flag bearing three chevronels, from the arms of Iestyn ap Gwrgant, the last ruler of the old Kingdom of Morgannwg (Glamorgan). The coalminer and steel worker were retained as the supporters of the arms, but with their positions reversed. The motto A Ddioddefws A Orfu or "He who suffered, conquered" was also retained from Glamorganshire.
The first three maps are provided by A Vision of Britain through Time
These maps were found on Wikimedia Commons
These maps of Glamorgan post-1974 were found on another site and are very useful for sorting out the up-to-date geography of the area