Mid Sussex is a local government district in West Sussex, England. The largest town is Haywards Heath, where the council is based. The district also contains the towns of Burgess Hill and East Grinstead plus surrounding rural areas, including many villages. The district includes part of the South Downs National Park and part of the designated Area of Outstanding Natural Beauty of High Weald, including sections of Ashdown Forest. The district contains most headwaters of the River Ouse. Its largest body of water is Ardingly reservoir which is used by watersports clubs. At the 2021 census the district had a population of 152,949.

The neighbouring districts are Crawley, Horsham, Brighton and Hove, Lewes, Wealden and Tandridge.

The name "Mid Sussex" was occasionally used for various parts of central Sussex prior to 1974, including as an alternative name for the Lewes constituency created under the Redistribution of Seats Act 1885, and as a joint water district established in 1907.^[2]

The modern district was formed on 1 April 1974 under the Local Government Act 1972 as one of seven districts within West Sussex. The new district covered the whole area of three former districts and most of a fourth, which were all abolished at the same time:^[3][4]

• Burgess Hill Urban District
• Cuckfield Urban District (included Haywards Heath and Lindfield)
• Cuckfield Rural District (except the parts of the parishes of Slaugham and Worth within the designated area for the new town of Crawley)
• East Grinstead Urban District

The new district was named Mid Sussex, reflecting its position within the historic county.^[5] All of the areas which made up Mid Sussex were in East Sussex prior to 1974; as part of the reforms that year they were transferred to West Sussex. The change of county was not without controversy; the government's rationale for the change was that it brought the projected major economic area centred on Crawley and Gatwick Airport under the supervision of one county council.^[6]

Mid Sussex District Council provides district-level services. County-level services are provided by West Sussex County Council.^[9] The whole district is also covered by civil parishes, which form a third tier of local government.^[10]

In the parts of the district within the South Downs National Park, town planning is the responsibility of the South Downs National Park Authority. The district council appoints one of its councillors to serve on the 27-person National Park Authority.^[11]

The district is divided into 24 civil parishes. The parish councils for Burgess Hill, East Grinstead and Haywards Heath have declared their parishes to be towns, allowing them to take the style "town council". The small parish of Newtimber has a parish meeting rather than a parish council.^[21] Hassocks is a post town but has a parish council rather than a town council.

Homes owned by their occupants, with or without a loan, make up more than 85% of Mid Sussex housing. Mid Sussex's residents had the lowest burden of social housing, at 0.5% of housing stock, at the time of the census, a district which is approximately 30 minutes by its fast railway services from the area with the highest such proportion covering London Bridge station, the London Borough of Southwark (having 31.2% social housing) and from a creative and self-declared, progressive authority with 9.8% social housing and 28% of its housing privately rented, Brighton and Hove.

In terms of rented housing Mid Sussex at the 2011 census ranked 216th out of in terms of 327 local authorities in England. The proportion of homes which were rented as investments by non-occupants was higher than several other semi-rural districts of Sussex, with 11.7% of housing stock speculatively acquired in this way or to provide for those unable to obtain mortgage finance and 1.0% was let out to residents on either public or private shared ownership schemes, close to the national average. These figures are those of the 2011 census.^[22]

•  West Sussex portal