River Stour, river, eastern England, with a length of 47 miles (76 km). It rises in eastern Cambridgeshire and flows eastward through East Anglia, forming most of the county boundary between Suffolk and Essex, through country made famous by the paintings of the artist John Constable. The Stour enters the North Sea at Harwich by a tidal estuary. Several other and less important English rivers have the same name.