The town lies in the valley of the River Waveney, around a mere (lake) that covers . The mere is up to deep, although there is another of mud. The town takes its name from dic an Anglo-Saxon word meaning either ditch or embankment.
Diss has a large number of historic buildings, including the early 14th century parish church. It is also home to a museum. Diss railway station lies on the Great Eastern Main Line route from London to Norwich.