The London Borough of Barnet is a local authority area on the northern outskirts of London. The borough was formed in 1965 from parts of the ceremonial counties of Middlesex and Hertfordshire. It is the second largest London borough by population with 389,344 inhabitants as of 2021, also making it the 17th largest district in England. The borough covers an area of 86.74 square kilometres (33 sq mi), the fourth highest of the 32 London boroughs, and has a population density of 45.8 people per hectare, which ranks it 25th.

Middlesex was a county in southeast England. Its area was almost entirely within the wider urbanised area of London and mostly within the ceremonial county of Greater London, with small sections in neighbouring ceremonial counties. The county's boundaries largely followed three rivers: the Thames in the south, the Lea to the east and the Colne to the west. A line of hills formed the northern boundary with Hertfordshire.