Gillingham is a town in the unitary authority

Unitary authority

A unitary authority is a type of local authority that has a single tier and is responsible for all local government functions within its area or performs additional functions which elsewhere in the relevant country are usually performed by national government or a higher level of sub-national...

 of Medway

Medway

Medway is a conurbation and unitary authority in South East England. The Unitary Authority was formed in 1998 when the City of Rochester-upon-Medway amalgamated with Gillingham Borough Council and part of Kent County Council to form Medway Council, a unitary authority independent of Kent County...

 in South East England

South East England

South East England is one of the nine official regions of England, designated in 1994 and adopted for statistical purposes in 1999. It consists of Berkshire, Buckinghamshire, East Sussex, Hampshire, Isle of Wight, Kent, Oxfordshire, Surrey and West Sussex...

. It is part of the ceremonial county

Ceremonial counties of England

The ceremonial counties are areas of England to which are appointed a Lord Lieutenant, and are defined by the government as counties and areas for the purposes of the Lieutenancies Act 1997 with reference to the metropolitan and non-metropolitan counties of England and Lieutenancies Act 1997...

 of Kent

Kent

Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...

. The town includes the settlements of Brompton, Hempstead

Hempstead, Kent

Hempstead is a settlement near Gillingham, Kent, part of the urban area of the Medway Towns.-Location and geography:It is located on the southern edge of the borough of Medway adjacent to Wigmore and Lordswood and linked to Gillingham and the M2 by the A278 trunk road.Most of Hempstead is in a...

, Rainham

Rainham, Medway

The town of Rainham is a part of the Medway Towns conurbation, under the unitary authority of Medway, in South East England, and part of the ceremonial county of Kent. Historically, Rainham was a separate village until, in 1928, it was added to the Municipal Borough of Gillingham, which had itself...

, Rainham Mark and Twydall

Twydall

Twydall is the home of Oliver Newman in an area of Gillingham in Medway, in the ceremonial county of Kent, England. It is near junction 4 of the M2 motorway. The origin of the name Twydall is thought to mean “Two Parts” or “Double Portion” from the Old English twidǣl, but by 1240 it was written...

.

Gillingham means a homestead of Gylla's family, from Old English ham (village, homestead) and ingas (family, followers), and was first recorded in 10th century as Gyllingeham.

Also referred to in old texts as Jillyingham Water, hence the pronunciation being Gillingham (the G sounds as a "J" as in the girls' name Jill).
Gillingham became an urban district

Urban district

In the England, Wales and Ireland, an urban district was a type of local government district that covered an urbanised area. Urban districts had an elected Urban District Council , which shared local government responsibilities with a county council....

 under the Local Government Act 1894

Local Government Act 1894

The Local Government Act 1894 was an Act of the Parliament of the United Kingdom that reformed local government in England and Wales outside the County of London. The Act followed the reforms carried out at county level under the Local Government Act 1888...

, gaining municipal borough

Municipal borough

Municipal boroughs were a type of local government district which existed in England and Wales between 1835 and 1974, in Northern Ireland from 1840 to 1973 and in the Republic of Ireland from 1840 to 2002...

 status in 1903.