The Borough of Onslow was a local government district immediately to the north of Wellington, New Zealand. Incorporated on 13 March 1890 it included the districts of: Wadestown, Crofton, Khandallah and Kaiwarra but not Johnsonville. It replaced the Kaiwarra Town Board, the Wellington District Roads Board and a small part of the very wide jurisdiction of the Hutt County Council. Johnsonville Town Board remained independent.