It borders Lancashire to the north, Greater Manchester to the east, Cheshire to the south, the Welsh county of Flintshire across the Dee Estuary to the southwest, and the Irish Sea to the west.

For local government purposes the county comprises five metropolitan boroughs: Knowsley, St Helens, Sefton, Wirral, and Liverpool.

What is now Merseyside was a largely rural area until the Industrial Revolution, when Liverpool and Birkenhead's positions on the Mersey Estuary enabled them to expand.

Liverpool became a major port, heavily involved in the Atlantic slave trade and in supplying cotton to the mills of Lancashire, and Birkenhead developed into a centre for shipbuilding.

Instead, a Royal Commission was set up to review English local government entirely, and its report (known as the Redcliffe-Maud Report) proposed a much wider Merseyside metropolitan area covering southwest Lancashire and northwest Cheshire, extending as far south as Chester and as far north as the River Ribble.

In 1970 the Merseyside Passenger Transport Executive (which operates today under the Merseytravel brand) was set up, covering Liverpool, Sefton, Wirral and Knowsley, but excluding Southport and St Helens.

The Local Government Bill presented to Parliament involved a substantial trimming from the White Paper, excluding the northern and southern fringes of the area, excluding Chester, Ellesmere Port, and, for the first time, including Southport, whose council had requested to be included.

Merseyside contains green belt interspersed throughout the county, surrounding the Liverpool urban area, as well as across the Mersey in the Wirral area, with further pockets extending towards and surrounding Southport, as part of the western edge of the North West Green Belt.

[8] Merseyside comprises the metropolitan boroughs of Liverpool, Knowsley, Sefton, St Helens and Wirral.

The Liverpool City Region Combined Authority, which includes the five boroughs of Merseyside and the Borough of Halton in Cheshire, oversees functions given to it under the area's devolution deal with the UK government, such as transport, housing, innovation, employment, energy, tourism, and trade, and some responsibilities relating to crime and justice.

[9][10] The combined authority is led by the Mayor of the Liverpool City Region, Steve Rotheram, who was elected in 2017 and re-elected in 2021[11] and in 2024.

The Mersey Gateway Bridge opened in 2017 and is designed to improve transport links between Widnes and Runcorn and other key locations in the vicinity.

[19][20] Merseyrail is the county's urban rail system and is operated by Merseytravel, the combined passenger transport executive for the Liverpool City Region.

[30] It serves more than 100 global destinations including Africa, Australia, China, India, the Middle East and South America.

[31][32] A second container terminal, Liverpool2 at Seaforth, can handle Post-Panamax vessels and doubled the port's capacity when it opened in 2016.

[35][36][37] The airport is planning substantial expansion, and is forecast to handle more than 12 million passengers by 2030, as well as targeting permanent direct long haul flights and significantly larger terminal facilities.

Aintree Motor Racing Circuit hosted the British Grand Prix biennially between 1955 and 1961, and finally in 1962.