's map of the County Palatine of Lancaster, 1610
The county was established in 1182, later than many other counties. During Roman times the area was part of the Brigantes tribal area in the military zone of Roman Britain. The towns of Manchester, Lancaster, Ribchester, Burrow, Elslack and Castleshaw grew around Roman forts. In the centuries after the Roman withdrawal in 410AD the northern parts of the county probably formed part of the Brythonic kingdom of Rheged, a successor entity to the Brigantes tribe. During the mid-8th century, the area was incorporated into the Anglo-Saxon Kingdom of Northumbria, which became a part of England in the 10th century.
In the Domesday Book, land between the Ribble and Mersey were known as "Inter Ripam et Mersam" and included in the returns for Cheshire. Although some historians consider this to mean south Lancashire was then part of Cheshire, it is by no means certain.[note 1][note 2] It is also claimed that the territory to the north formed part of the West Riding of Yorkshire. It bordered on Cumberland, Westmorland, Yorkshire, and Cheshire.
The county was divided into hundreds, Amounderness, Blackburn, Leyland, Lonsdale, Salford and West Derby. Lonsdale was further partitioned into Lonsdale North, the detached part north of the sands of Morecambe Bay including Furness and Cartmel, and Lonsdale South.
Lancashire is smaller than its historical extent following a major reform of local government. In 1889, the administrative county of Lancashire was created, covering the historic county except for the county boroughs such as Blackburn, Burnley, Barrow-in-Furness, Preston, Wigan, Liverpool and Manchester. The area served by the Lord-Lieutenant (termed now a ceremonial county) covered the entirety of the administrative county and the county boroughs, and was expanded whenever boroughs annexed areas in neighbouring counties such as Wythenshawe in Manchester south of the River Mersey and historically in Cheshire, and southern Warrington. It did not cover the western part of Todmorden, where the ancient border between Lancashire and Yorkshire passes through the middle of the town.
During the 20th century, the county became increasingly urbanised, particularly the southern part. To the existing county boroughs of Barrow-in-Furness, Blackburn, Bolton, Bootle, Burnley, Bury, Liverpool, Manchester, Oldham, Preston, Rochdale, Salford, St. Helens and Wigan were added Blackpool (1904), Southport (1905), and Warrington (1900). The county boroughs also had many boundary extensions. The borders around the Manchester area were particularly complicated, with narrow protrusions of the administrative county between the county boroughs – Lees urban district formed a detached part of the administrative county, between Oldham county borough and the West Riding of Yorkshire.
By the census of 1971, the population of Lancashire and its county boroughs had reached 5,129,416, making it the most populous geographic county in the UK. The administrative county was also the most populous of its type outside London, with a population of 2,280,359 in 1961. On 1 April 1974, under the Local Government Act 1972, the administrative county was abolished, as were the county boroughs. The urbanised southern part largely became part of two metropolitan counties, Merseyside and Greater Manchester. The new county of Cumbria incorporates the Furness exclave.
The boroughs of Liverpool, Knowsley, St. Helens and Sefton were included in Merseyside. In Greater Manchester the successor boroughs were Bury, Bolton, Manchester, Oldham (part), Rochdale, Salford, Tameside (part), Trafford (part) and Wigan. Warrington and Widnes, south of the new Merseyside/Greater Manchester border were added to the new non-metropolitan county of Cheshire. The urban districts of Barnoldswick and Earby, Bowland Rural District and the parishes of Bracewell and Brogden and Salterforth from Skipton Rural District in the West Riding of Yorkshire became part of the new Lancashire. One parish, Simonswood, was transferred from the borough of Knowsley in Merseyside to the district of West Lancashire in 1994. In 1998 Blackpool and Blackburn with Darwen became independent unitary authorities, removing them from the non-metropolitan county but not from the ceremonial county.
The Wars of the Roses tradition continued with Lancaster using the red rose symbol and York the white. Pressure groups, including Friends of Real Lancashire and the Association of British Counties advocate the use of the historical boundaries of Lancashire for ceremonial and cultural purposes.