King William Street is the part of a major arterial road that traverses the CBD and centre of Adelaide (the capital of South Australia). It was named by the Street Naming Committee on 23 May 1837 after King William IV, the then reigning monarch, who died within a month. King William Street is 132 feet (40 m) wide, and is the widest main street of all the Australian State capital cities, which are significantly narrower by comparison. It is historically considered one of Adelaide's high streets, for its focal point of businesses, shops and other prominent establishments.
The Glenelg Tram runs the entire length of the street, with the northern end of the line continuing along North Terrace to the Entertainment Centre in Hindmarsh and the southern end continuing along its own off-road right-of-way to Glenelg. Tram travel north of South Terrace is free.
The name King William is applied several times to the continuous stretch of road that begins in the inner southern suburbs and terminates in North Adelaide. Where it runs through the Adelaide city centre, it is named "King William Street"; elsewhere it is named "King William Road". It starts in the south as King William Road, at the north edge of Heywood Park in Unley Park, and runs through Hyde Park and Unley to Greenhill Road. It runs through the south parklands (as Peacock Road), the Adelaide city centre (as King William Street) and continues north from North Terrace as King William Road to Brougham Place, North Adelaide. The road continues north to National Highway 1 as O'Connell Street, but the name King William is not again used. The northern section called King William Road (connecting the Adelaide city centre with North Adelaide) passes several of Adelaide's landmarks, including Government House, Elder Park, the Adelaide Festival Centre, Adelaide Oval and St Peter's Cathedral. The section from North Terrace over the Adelaide Bridge to Pennington Terrace was named King William Road at the opening of the bridge in 1877.