unitary authority, geographic and historic county of Lincolnshire, England, centred on the town of Grimsby on the River Humber estuary of the North Sea. Grimsby is the country's premier fishing port and a leading centre for food processing. Chemical plants and other industries lie along the Humber estuary. Grimsby is also the administrative and service centre for the unitary authority and provides the main shopping and educational facilities for the unitary authority and surrounding areas of northern Lincolnshire. The unitary authority also includes the neighbouring coastal resort of Cleethorpes to the east and Immingham Dock—one of Britain's most important ports for bulk cargoes—and other industrial installations to the west. Inland the rural countryside extends over the coastal flats to the lower slopes of the Lincolnshire Wolds. Area 74 square miles (192 square km). Pop. (2005 est.) 157,500.