Cumberland is one of the historic counties of England that existed from the 12th century until it was abolished for administrative purposes in 1974, with its territory merging with the neighbouring county of Westmorland and parts of Lancashire and Yorkshire to form the modern administrative county of Cumbria.
The first record of the term "Cumberland" appears in 945, when the Anglo Saxon Chronicle recorded that the area was ceded to Malcolm I of Scotland by King Edmund of England. At the time of the Domesday Book in 1086 most of the future county remained part of Scotland although some villages in the ancient district of Millom, which were the possessions of the Earl of Northumbria, were included in the Yorkshire section with the Furness region.
In 1092 King William Rufus of England invaded the Carlisle district, settling it with colonists. He created an Earldom of Carlisle, and granted the territory to Ranulf Meschyn. In 1133 Carlisle was made the see of a new diocese, identical with the area of the earldom. However, on the death of King Henry I in 1135, the area was regained by Scotland's King David I. He was able to consolidate his power and made Carlisle one of his chief seats of government, while England descended into a lengthy civil war. In 1157 Henry II of England resumed possession of the area from Malcolm IV of Scotland, and formed two new counties from the former earldom: Westmorland and "Carliol". The silver-mining area of Alston, previously associated with the Liberty of Durham, was also added to the new county of Carliol for financial reasons. By 1177 the county of Carliol was known as Cumberland. The border between England and Scotland was made permanent by the Treaty of York in 1237.
Further Social and Economic History
The Wikipedia article Cumbria provides more information on the history of Cumberland (and Westmorland) from the 12th to the 20th century.
Internal Boundaries and Subdivisions
The Wikipedia article Cumberland includes