Dismal Swamp is a locality in the Australian state of South Australia located about 361 kilometres (224 mi) south-east of the state capital of Adelaide and about 19 kilometres (12 mi) north-west of the municipal seat of Mount Gambier.
Boundaries for the locality were created in February 1999 for the “long established name.” The name Dismal Swamp was used as early as 1845 when Anthony Sutton used the name for an occupation license on land described as being near Tarpeena. A school with the name operated from 1948 to 1954.
Dismal Swamp is bounded on its east side by the Riddoch Highway which passes through the locality from north to south The Mount Gambier railway line which has been closed since 1995, passes from north to south through the locality. The site of the former Wandilo railway station is located just north of the locality‘s southern boundary with Wandilo. The former Glencoe branch line passed through what is now the locality from 1904 to 1959 from the junction with the Mount Gambier railway line in Wandilo to the terminus in Glencoe.
The principal land use in the locality is primary production. Three parcels of land have been proclaimed for conservation purposes as the Telford Scrub Conservation Park and as the native forest reserves respectively known as Grundy Lane and Wandilo.
Dismal Swamp is located within the federal division of Barker, the state electoral district of Mount Gambier and the local government area of the District Council of Grant.