region and former administrative county, eastern England, bordering the River Humber (Humber, River) estuary and the North Sea. The region comprises parts of the historic counties of Yorkshire and Lincolnshire to the north and south of the Humber, respectively. The area north of the Humber, sometimes known as North Humberside, forms the geographic county of East Riding of Yorkshire, which is divided administratively into the unitary authorities of East Riding of Yorkshire and Kingston upon Hull. Kingston upon Hull is the region's largest city and commercial centre. South Humberside, on the south side of the estuary, is part of the geographic county of Lincolnshire and is divided administratively into the unitary authorities of North Lincolnshire and North East Lincolnshire.