Lindsey survives into modern times as one of three Parts or traditional administrative subdivisions of the county of Lincolnshire, which is the second-largest county in England (after Yorkshire, which is also divided into three regions, called ridings). It is in the north, going up to the River Humber, and containing the city of Lincoln. It is slightly higher than the rest of Lincolnshire, as it contains the Lincoln Wolds. It is mainly wide-open farmland. To the south are the other two parts, Holland and Kesteven.
After the 1974 reorganization of local government, it ceased to be an administrative region. The northernmost parts on the banks of the Humber, including Grimsby and Scunthorpe, were grouped into the unloved and ill-fated "administrative county" of Humberside. There are now district councils called East Lindsey and West Lindsey.
The name Lindsey looks like it means island on the River Lindum, but the ending -eg (modern -ey) was normally only used for small islands, not the whole river-bounded region of Lindsey. The earlier form of the name is Lindisse, which is inconclusive. Source for this: www.roffe.freeserve.co.uk/lindsey.htm