 The Local Government Act 1888 constituted all municipal boroughs with a population of more than 50,000 as "county borough"s. Accordingly, the County Borough of Rochdale came into existence in 1889, with the powers of both a borough and a county council.Rochdale remained within Lancashire for certain purposes such as lieutenancy and administration of justice.In 1900 the county borough absorbed the bulk of the neighbouring Castleton Urban District by mutual agreement.