At the time of Domesday Book in 1086, parts of the county were considered either to form part of Yorkshire or to be within the separate Kingdom of Strathclyde. The Normans conquered the area that is now Cumbria in 1092 during the reign of William II and created the baronies of Kendal and Westmorland. These were originally distinct jurisdictions with separate sheriffs, but were formed into a single county of Westmorland in 1226/7. Before 1226 the Barony of Kendal was connected to the Earldom or Honour of Lancaster while that of Westmorland was part of the Earldom of Carlisle.
The historic county boundaries are with Cumberland to the north, County Durham and Yorkshire to the east, and Lancashire to the south and west. Windermere forms part of the western border with Lancashire north of the sands, and Ullswater part of the border with Cumberland.
The highest point of the county is Helvellyn at 3,117 ft (950m). According to the 1831 census the county covered an area of 485,990 acres (1,966.7 km2).
Appleby, the historic county town, formed a historic borough and was not reformed by the Municipal Corporations Act 1835, although reform came in 1885. Kendal was reformed as a municipal borough in 1835.