The historic county consisted of two separate parts. The main part runs along the northwestern coast of England. When it included Manchester and Liverpool it had a greatest length of 76 miles, and breadth of 45 miles, and an area of 1,208,154 acres. The northern detached part of the old county palatine, consisting of Furness and Cartmell was 25 miles in length, 23 miles in breadth and was separated from the main portion of Lancashire by Morecambe Bay and the Kendal district of Westmorland. Administratively it has now joined Westmorland as part of modern Cumbria. This district reaches a peak height of 2633 ft at Old Man of Coniston, the highest in England.
As a county palatine, the Duke of Lancaster had sovereignty rights in the areas of justice and administration within the county. However, in 1461 Edward IV decreed that the county palatine should become part of the Duchy of Lancaster and from 1471 the offices of Chancellor of the Duchy and Chancellor of the Palatinate were held by the same person. The administrative centre moved to London, while Lancaster remained the legal centre. Under the Supreme Court of Judicature Act 1873 the common law and criminal jurisdictions transferred to the new High Court of Justice. After November 1875 the palatinate consisted only of the Court of Chancery and the Chancellor's right to appoint justices of the peace and other local officers. Under the Courts Act 1971, the Court of Chancery also merged with the High Court. And in March 2005, under the Courts Act 2003, the power to appoint magistrates in Lancashire, Greater Manchester and Merseyside transferred to the Ministry of Justice. The High Sheriffs of Lancashire, Greater Manchester and Merseyside are still appointed by the Queen in right of the duchy. The duchy also benefits from the legal concept of bona vacantia within county palatine, whereby it has the right to property for which the legal owner cannot be found. The proceeds are divided between two registered charities, the Duchy of Lancaster Benevolent Fund and the Duchy of Lancaster Jubilee Trust.
The emblem of the historic county of Lancashire is the Red Rose of the English royal House of Lancaster, and in 2008 the Flag of Lancashire became recognised by the Flag Institute. On 27 November, Lancashire Day celebrates the culture of the historic county ranging from its history to its own dialect.
Lancashire takes its name from the city of Lancaster, whose name means 'Roman fort on the River Lune', combining the name of the river with the Old English cæster, which derived from the Roman word for a fort or camp. Official documents called it the "County of Lancaster" rather than Lancashire, "Lancastershire" occurs in late 14th century and Leland, was still using it in 1540. "Lancashire" occurs in the Paston Letters in 1464. Lancashire became the preferred designation, as a syncope of Lancastershire.
At the time when the Romans arrived in England, much of northern England was inhabited by the Brigantes, though the Cumbrian highland area was inhabited by the Carvetii, who were possibly a tribe within the larger Brigantes group. Another tribe named the Setantii has also been hypothesized based on the name of a Roman era port near the mouth of the River Wyre, called Portus Setantiorum, and they were possibly also Brigantes, if they existed.