The station opened on 17 September 1886 as
Hornsby, but was renamed
Hornsby Junction on 1 November 1894. This was due to the construction of
Normanhurst station to the south, which was initially named Hornsby as it was located in what was the more densely populated area of Hornsby at the time. Naming the station Hornsby Junction was an attempt to avoid confusion, but it was realised that having two Hornsby stations was still very confusing. On 1 May 1900, the suburb and station to the south was renamed Normanhurst, and Hornsby Junction reverted to
Hornsby. On 1 January 1890, Hornsby became a
junction station with the opening of the
North Shore line to
St Leonards. In 1894, a third platform was built along with a locomotive depot to the east of the station. Hornsby was the northern extremity of the electrified network from 1930 until it was extended to
Gosford in 1960. The wires did continue north of the station as far as the
Hornsby Maintenance Depot. The station was extensively upgraded in 1986, including tiling of the platform, the addition of shelters and the modification of the southern concourse. The southern concourse was again extensively modified sometime between April 1994 and October 1995 to include brick lift shafts and accessibility to each platform. As part of the
CityRail Clearways Project, a fifth platform was constructed for use by through northbound trains. To allow for the new line, the Hornsby Signal Box was shifted 120 metres in 2007. The new platform opened on 16 March 2009, with the existing Platform 4 becoming a turnback platform for Northern line trains. The additional platform allows extra trains to run on the Northern line via the
Epping to Chatswood line and improves reliability. As Hornsby is both an originating and terminating point for some services, on 10 July 2003 the communications system in a
Millennium Train failed because the train's software could not compute that the origin and destination of the service had the same name. ==Platforms and services==