Original: Under the Local Government Act 1972, the county boroughs and administrative county of Glamorgan were abolished on 1 April 1974, with three new counties being established, each containing a former county borough - West Glamorgan, Mid Glamorgan, South Glamorgan.
Simplified: The administrative county of Glamorgan existed until April 1, 1974. It was replaced with three new counties called Mid Glamorgan, South Glamorgan and West Glamorgan.