From the Wikipedia page
Uxbridge was, from 1875 to 1925, a local government district] in Middlesex.
The district was formed as a rural sanitary district in 1875. It was based on the existing Uxbridge Poor Law Union, except for Uxbridge, to the west, which was an urban sanitary district. Part of the Hillingdon parish was added to Uxbridge USD in 1883. The parish of Northwood was removed in 1891, forming an urban sanitary district.
Under the Local Government Act 1894 it became a rural district, with a directly elected rural district council. The Hillingdon parish was split, with Hillingdon West being formed from the part in Uxbridge urban district and Hillingdon East being the part in the rural district.
As of 1894, the district included the parishes of
A further parish, Yiewsley, was created in 1896 from part of the Hillingdon East parish.
Hayes became an urban district in 1904, as did Ruislip (under the name Ruislip-Northwood). Northolt was split in 1928 between the Municipal Borough of Ealing and Harrow on the Hill Urban District. A Yiewsley Urban District was created in 1911.
The district was finally abolished in 1929, becoming part of the Uxbridge Urban District, apart from the parish of West Drayton which became part of the renamed Yiewsley and West Drayton Urban District. Most of the area now forms part of the London Borough of Hillingdon, with the former parish of Northolt split between the London Borough of Ealing and the London Borough of Brent.