Hillingdon, outer borough (1991 pop. 225,800) of Greater London, SE England. Industries include printing, motion-picture production, and the manufacture of aircraft, food products, and electrical and musical instruments. Hillingdon comprises a portion of London (Heathrow) Airport and part of the Grand Union Canal, which links the coalfields and other sources of raw materials in the Midlands with London. Within the borough, Uxbridge was an ancient market town on the Colne River. Charles I and Parliament representatives negotiated unsuccessfully in the "Treaty House" in Uxbridge in 1645. The parish church in Hayes was used by St. Anselm, archbishop of Canterbury.