The River Don is a river in South Yorkshire and the East Riding of Yorkshire, England. It rises in the Pennines, west of Dunford Bridge, and flows for 69 miles eastwards, through the Don Valley, via Penistone, Sheffield, Rotherham, Mexborough, Conisbrough, Doncaster and Stainforth. It originally joined the Trent, but was re-engineered by Cor…The River Don is a river in South Yorkshire and the East Riding of Yorkshire, England. It rises in the Pennines, west of Dunford Bridge, and flows for 69 miles eastwards, through the Don Valley, via Penistone, Sheffield, Rotherham, Mexborough, Conisbrough, Doncaster and Stainforth. It originally joined the Trent, but was re-engineered by Cornelius Vermuyden as the Dutch River in the 1620s, and now joins the River Ouse at Goole. Don Valley is a UK parliamentary constituency near the Doncaster stretch of the river.