It was formerly a parish in the county of Middlesex covering the neighbouring areas of Eastcote, Northwood, Ruislip Manor and South Ruislip. The parish appears in the Domesday Book, and some of the earliest settlements still exist today, designated as local heritage sites. The parish church, St Martin's, dates back to the 13th century and remains in use. The buildings at the northern end of Ruislip High Street form the core of the original village square and are now Grade II listed. It originally featured a central water pump which was moved out of the road in the 1970s as a result of increased traffic.
The expansion of the Metropolitan Railway in the early 20th century acted as a catalyst for development in the area. A station was opened in Ruislip in 1904 and the parish council created a new urban district to address the forthcoming population growth. The Ruislip-Northwood Urban District continued until 1965 when Ruislip became part of the newly established London Borough of Hillingdon. Between 1911 and 1961, Ruislip-Northwood experienced a significant rise in population, from 6,217 to 72,791, largely attributed to the extension of the railway.
Major landmarks in the area include Ruislip Lido, a former reservoir, now an area of public parkland with its own miniature railway and Manor Farm, a settlement dating from the 9th century which is now designated as a local heritage site. Ruislip is included within the Ruislip, Northwood and Pinner Parliament constituency and is covered by three electoral wards within the local council.
Ruislip is one of the ancient parishes of Middlesex. From 1894 to 1904 it was part of Uxbridge Rural District and from 1904 to 1965 it was administered as Ruislip Northwood Urban District. In 1965 civil parishes in the newly-created Greater London were abolished and the former territory of Ruislip became part of the London Borough of Hillingdon.