Northumberland is the northernmost ceremonial county and a unitary district in North East England. It borders Cumbria to the west, County Durham to the south and Tyne and Wear to the southeast and the Scottish Borders council area to the north. Its North Sea coastline is a designated Area of Outstanding Natural Beauty with a 64-mile (103 km) long distance path. Since 1981, the county council has been located in Morpeth, situated in the east of the county.

The historical boundaries of the county of Northumberland included Newcastle upon Tyne, the traditional county town, as well as Tynemouth and other settlements in North Tyneside, all areas transferred to Tyne and Wear in 1974 under the Local Government Act 1972. The historical county boundaries are sometimes taken to exclude Islandshire, Bedlingtonshire and Norhamshire (collectively North Durham), exclaves of County Durham which were incorporated into Northumberland in 1844. For Eurostat purposes Northumberland is a NUTS 3 region (code UKC21) and is one of three local authority areas that comprise the "Northumberland and Tyne and Wear" NUTS 2 region.

Being on the border of England and Scotland, Northumberland has been the site of a number of battles. The county is noted for its undeveloped landscape of high moorland, a favourite with landscape painters, and now largely protected as a National Park. Northumberland is the most sparsely populated county in England, with only 62 people per square kilometre.