It was incorporated in 1965 by bringing together the Middlesex Borough of Uxbridge with the Urban Districts of Hayes & Harlington, Ruislip-Northwood and Yiewsley & West Drayton. Denham is in Buckinghamshire but served by Middlesex postally.

There was such a row between the top half and the bottom half of the proposed new authority as to what to call it that at one time it was going to be known as the Borough of West Middlesex. In the end the steering committee plumped diplomatically for the parish in the middle of them all, Hillingdon!