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" In 1889, the administrative county of Lancashire was created, covering the historical county except for the county boroughs such as Blackburn, Burnley, Barrow-in-Furness, Preston, Wigan, Liverpool and Manchester.
The land that lay between the Ribble and Mersey, Inter Ripam et Mersam, was included in the returns for Cheshire.
When its boundaries were established, it bordered Cumberland, Westmorland, Yorkshire, and Cheshire.
The county was subject to a significant boundary reform in 1974 that removed Liverpool and Manchester and most of their surrounding conurbations to form the metropolitan counties of Merseyside and Greater Manchester.
Blackpool was a centre for tourism for the inhabitants of Lancashire's mill towns, particularly during wakes week.
The county contained several mill towns and the collieries of the Lancashire Coalfield.
By the 1830s, approximately 85% of all cotton manufactured worldwide was processed in Lancashire.
The county palatine boundaries remain the same as those of the pre-1974 county, with the Duke of Lancaster exercising sovereignty rights, later than many other counties.
During Roman times the area was part of the Brigantes tribal area in the military zone of Roman Britain.
During the 20th century, the county became increasingly urbanised, particularly the southern part.