Gillingham (/ˈdʒɪlɪŋəm/ ^ⓘ JIL-ing-əm) is a town in Kent, England, which forms a conurbation with neighbouring Chatham, Rochester, Strood and Rainham. It is the largest town in the borough of Medway and in 2022 had a population of 111,033.

Gillingham's name is of Old English origin, derived from the personal name Gylla (or Gilla) combined with the suffixes -ingas (meaning "the people of" or "family") and -hām ("homestead," "village," or "estate"). Taken together, the name translates to "the homestead of Gylla's people". The names of Gillingham in Dorset and Gillingham in Norfolk have the same etymology, despite the differing pronunciation. Early recordings of the name appear in the Domesday Book (1086) as Gelingeham for Kent.

Before 1894, Gillingham was governed by the parish vestry, Court Leet, and from 1873, a local Board of Health. By 1891, the parish spanned about 5,000 acres with roughly 21,000 residents. The 1894 Local Government Act replaced the Board of Health with the Gillingham Urban District Council, an elected body responsible for local services. The UDC initially had 15 members, three wards (Old Brompton, New Brompton, and Gillingham), and met on Gardiner Street. Key figures included R. H. Cock (chairman), F. C. Boucher (clerk), and the Featherby family, George Featherby, a former brickmaker and councillor, was succeeded by his son John Robert Featherby, who became chairman in 1899. He led the effort for borough status, and when Gillingham became a municipal borough in 1903, J. R. Featherby became its first mayor, and the UDC was dissolved.

After the urban district council was dissolved, Gillingham Borough Council became the local authority body for the area, operating from 1903 until 1 April 1998. It was established by royal charter on 17 August 1903, evolving from the earlier Gillingham Urban District Council, and John Robert Featherby served as its first mayor. The council governed local services for Gillingham and, from 1928, the adjoining parish of Rainham, after its boundaries were expanded.

Unlike neighbouring Medway towns during the 1974 local government reorganisation, Gillingham chose to remain independent as a non‑metropolitan district under Kent County Council, handling local planning, housing and community services, while the county oversaw broader functions.

The council managed local development, infrastructure improvements and civic facilities throughout the 20th century. It was finally abolished in 1998, when it merged with Rochester‑upon‑Medway City Council to form the Medway unitary authority, known today as Medway Council.

The Municipal Buildings in Canterbury Street were built as council offices for Gillingham Borough Council. They were opened by the Lord Mayor of London, Sir George Broadbridge, on 25 September 1937. The Lord Mayor was received at Gillingham Railway Station by a guard of honour of boys of HMS Arethusa. Before the Second World War, air raid sirens were placed on the Municipal Buildings, and the local Civil Defence headquarters were in a single-storey building, to the rear of the car park. In about 1953, beneath part of the car park, Gillingham Borough Control Centre was built underground.

When Gillingham Borough Council later merged with Rochester upon Medway to form the unitary Medway Authority in 1998, the buildings were still used as council offices and for meetings for several years afterwards. Later, Medway Council then moved into the former Lloyd's of London headquarters at Chatham Gun Wharf, and the Municipal Buildings were considered surplus to requirements. They were sold off in 2008 under a contract which turned them into a residential care home.