Horsham is a local government district in West Sussex, England. It is named after the town of Horsham, which is its largest settlement and where the council is based. The district also includes the surrounding rural area and contains many villages, the largest of which are Southwater and Billingshurst. The district includes part of the South Downs National Park and part of the designated Area of Outstanding Natural Beauty of High Weald. At the 2021 census the district had a population of 147,487.

The neighbouring districts are Crawley, Mid Sussex, Brighton and Hove, Adur, Arun, Chichester, Waverley and Mole Valley.

Horsham itself had been an ancient borough from the thirteenth century, but lost its borough status in the 1830s. The town had been made a local government district in 1875, which became Horsham Urban District in 1894.

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, which were all abolished at the same time:

The new district was named Horsham, after its largest settlement.

Horsham District Council provides district-level services. County-level services are provided by West Sussex County Council. All of the district is covered by civil parishes, which form a third tier of local government for their areas.

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.

The council has been under Liberal Democrat majority control since the 2023 election.