Hornsey was an ancient parish in the county of Middlesex. It was both a civil parish, used for administrative purposes, and an ecclesiastical parish of the Church of England.
Hornsey Parish was probably formed in about the thirteenth century at the time a church was built in the village of Hornsey. The Parish fell within the Ossulstone Hundred of Middlesex, and in later times it was part of the Finsbury division of the Hundred. The Hornsey Parish boundary ran from Stoke Newington, in the south, through Stroud Green to Highgate in the west, and from near Colney Hatch in the north, past Muswell Hill, and a detached portion of Clerkenwell Parish, eastwards to the Tottenham Parish border and then along Green Lanes back to Stoke Newington. In the north a field called Hornsey Detached No.1 stretched up to Colney Hatch and at the southern end there were another two fields, Hornsey Detached Nos. 2 and 3 by Newington Green. The parish also owned another field in Canonbury, Islington, which was surrendered to the Parish by Sir Thomas Draper, Bt., in 1668.
The vestry of the parish was entrusted with various civil administrative functions from the 17th century. Unusually the parish was divided between the Highgate (upper) side and the Hornsey (lower) side, and separate vestry officers appointed for each side. After 1837 the civil administration changed. The Hornsey vestry established a Public Health and Drainage committee in1851; this committee only had a short life as it was replaced, in 1854, with a Highways Board, and a full Local Board was established in 1867. The Local Board gave way to the Urban District Council in 1894/5 which governed the Parish until 1903, when it became obtained Borough status. By this time South Hornsey had separated and become an autonomous local authority from Hornsey, which had become part of the Poor Law Union of Edmonton.