The London Borough of Hillingdon ( pronunciation (help·info)) is the westernmost borough in Greater London, England which had a population of 273,936 based on the 2011 Census. and was formed from the districts of Ruislip-Northwood, Uxbridge, Hayes and Harlington and Yiewsley and West Drayton in the historic county of Middlesex. Today, Hillingdon is home to Heathrow Airport and Brunel University, and is the second largest of the 32 London boroughs by area.

Hillingdon Council governs the borough, with its headquarters in the Civic Centre in Uxbridge. For administrative purposes, the borough is split into North and South Hillingdon with more industrial units to the south and residential suburban areas in the north. Much of the residential areas were expanded with the extension of the Metropolitan Railway from Harrow on the Hill to Uxbridge in the early 1900s and the gradual establishment of stops along the line, becoming known as "Metro-land".