River Don, Yorkshire Wikipedia. The River Don (also called Dun in some stretches) is a river in South Yorkshire and the East Riding of Yorkshire, England.It rises in the Pennines and flows for 70 miles (110 km) eastwards, through the Don Valley, via Penistone, Sheffield, Rotherham, Mexborough, Conisbrough, Doncaster and Stainforth.It originally joined the Trent, but was reengineered by ...