The park was started in 1932 by Billy Butlin on the site of the old east bank fort and windmill It was easily spotted from a distance by the presence of a large roller coaster on the roof known as "The Wild Mouse". Early pictures of this can be viewed in the West Sussex past pictures archive reference numbers PP/WSL/PC005524 & PP/WSL/TC001729. A picture of the old site prior to construction is also available reference number PP/WSL/PC005512.
During the war the park closed from 1941 to 1945, and the building was used for storage and the gathering of troops going overseas. The building suffered bomb damage during that time; but was repaired and reopened after the war as part of the Butlin's Empire, that were later purchased by the Rank Organisation.
In 1977, the park was bought from the Rank Organisation by the Billy Smart Circus family and was renamed Smart's Amusement Park. They set about re-equipping it into a family Amusement centre with a selection of indoor rides, including a hall of mirrors
In 1994 the current owner, Gary Smart oversaw a sizable redevelopment of the site. The name changed from Smart’s Amusement Park to the contemporary Harbour Park, which reflected the theme running throughout the site and its unique location on the seafront and riverside. Over the next few years major works were undertaken and the final phase was completed in the year 2000. The roller coasters were removed during this time.
Harbour Park entered the new millennium with a new look, whilst managing to retain the Smart family values of providing a friendly, fun and entertaining family venue. In fact, Billy Smart still watches over the park in the form of a magnificent bronze statue located in the main building.