town and seaport, unitary authority of North East Lincolnshire, historic county of Lincolnshire, eastern England. Although it was important as a medieval market town near a small harbour on the River Humber estuary, 6 miles (10 km) from the North Sea, Grimsby initially failed to develop as a port. In 1800, however, the diversion of the small River Freshney into a dock north of the town solved the problem of silting, and Grimsby became a fishing port. Railway access in the mid-19th century stimulated the extension of docks beyond the foreshore and toward the channel. Grimsby is the country's premier fishing port and a leading centre for food processing. Chemical factories and other industries lie along the Humber estuary. Grimsby is also an administrative and service centre and provides the main shopping and educational facilities for much of northern Lincolnshire. Pop. (2001) 87,574.