Thamesdown covered the areas of the municipal borough of Swindon and the neighbouring Highworth Rural District (which had been created in 1894), which were both abolished at the same time.

[5] On 1 April 1997 Thamesdown was made a unitary authority, making it administratively independent from Wiltshire County Council.

[6] In June 1996, during the transition period to becoming a unitary authority, the council passed an order that the area would be renamed Swindon with effect from 1 April 1997 as well.

The borough encompasses the Swindon urban area and surrounding countryside to the north, east and south, including the town of Highworth.

[12][13] The two Central parishes fall within the boundaries of the town and former municipal borough, divided along the Great Western Main Line railway.