Horsham is a market town on the upper reaches of the River Arun on the fringe of the Weald in West Sussex, England. The town is 31 miles s…Horsham is a market town on the upper reaches of the River Arun on the fringe of the Weald in West Sussex, England. The town is 31 miles south south-west of London, 18.5 miles north-west of Brighton and 26 miles north-east of the county town of Chichester. Nearby towns include Crawley to the north-east and Haywards Heath and Burgess Hill to the south-east. It is the administrative centre of the Horsham district.