[15] On 28 January 1819, a delegation led by colonial official Sir Stamford Raffles anchored off St John's, a day before they arrived at mainland Singapore to establish a British trading port.

It was also tasked to operate the flagstaff to report ship sightings to the signal post on Government Hill in mainland Singapore.

[17][a] By 1830, the facilities on St John's Island, including the flagstaff, were reported by the officer in charge of public works to be in a dilapidated state.

[17] Visitors to the island in subsequent years such as naturalist George Bennett and Dr Robert Little found it to be virtually abandoned, with only one Malay inhabitant.

[21][22] As the number of immigrants to Singapore increased from the late 19th century onwards, the risk of epidemics heightened, leading to the establishment of a Quarantine Centre on St John's.

[26] However, in July 1873, a boat from Bangkok caused a cholera epidemic that lasted two months and resulted in 857 infections and 448 deaths, despite the orders of Governor Harry Ord to quarantine all ships from Siam.

[26] Consequently, Acting Master Attendant Henry Ellis proposed that a quarantine station be constructed on St John's Island.

[28] The St John's Island quarantine station opened in November 1874 and served not just immigrants to Singapore but also Muslims returning to Malaya after their pilgrimage to Mecca.

Although Ellis had plans for a police ship, a hospital on St John's, a steam cutter, and a cemetery on Kusu Island to support the quarantine station, it consisted largely of attap huts when first completed.

[29][30] The month it opened, the station quarantined more than 1,000 Chinese passengers on the cholera-infected SS Milton which was travelling from Swatow to the British colonies Penang and Province Wellesley.

[37] By 1930, the quarantine station was capable of vaccination and was equipped with a dispensary, telephone wires, and disinfection buildings with Izal solution spray.

[44] The St John's quarantine station officially closed on 14 January 1976 because the popularisation of air travel had drastically reduced the number of arrivals by boat.

[47][48] In August 1914, right after World War I began, most German men in Singapore were interned on St John's Island and Tanglin Barracks while women and children were detained in Kuala Lumpur.

Shortly after, the Japanese women and children in Singapore were also interned on St John's Island from late 1941 to 1942 before being shipped to Calcutta.

[48] The Malayan Emergency (1948–1960) sparked by the Communist Party of Malaya caused St John's to resume operating as a detention centre for political prisoners.

[59] Expecting an influx of political prisoners, St John's Island was officially announced as the site of the new detention centre on 3 July 1948 and became a protected area from 10 September onward.

[63] Singaporean political prisoners detained on St John's Island were university students, teachers, newspaper editors, several future politicians of Singapore, and others.

[64][65] Among the detainees were Devan Nair, Fong Swee Suan and Lim Chin Siong, all People's Action Party (PAP) members.

[67] The state's fear of communism did not abide, resulting in St John's being used as a detention centre for most of the detainees arrested during the anti-communist Operation Coldstore.

[81] In the 1950s, the government tackled drug activity more aggressively through legal means, vice operations, and the establishment of an Opium Treatment Centre on St John's.

They revised the Dangerous Drugs Ordinance of 1951 in 1953 to increase their authority to prosecute opium-related crimes, and initiated vice operations, such as the major opium crackdown of 1952.

[82][83][84][85] The Opium Treatment Centre was established under an amendment to the Dangerous Drugs Ordinance in 1954, marking the colonial government's first attempt to rehabilitate addicts.

[78] The subsequent rehabilitation phase would last six months to a year at the Opium Treatment Centre on St John's Island, during which patients were taught new skills such as carpentry to aid future reintegration into society.

[87][78] The experimental opium rehabilitation programme was noteworthy for medical institutions and was later claimed to cure the majority of those admitted; however, its criteria of admittance were controversial.

[97] In 1998, there was a rise in arrests of illegal immigrants and overstayers after the 1997 Asian Financial Crisis, and the government was anticipating a mass of Indonesian refugees after the May 1998 riots of Indonesia.

[104] Thus, the government began constructing a temporary Prison Detention Centre on St John's Island to house potential spill over illegal immigrants and drug addicts.

[109] However, proposals to redevelop St John's as a holiday island with restaurants, golf courses and an integrated resort-casino fell through.

[111] In April 2018, traces of asbestos was found in construction debris around the island's campsite, lagoon and holiday bungalow areas.

St John's coastline comprises sandy beaches, quarry rocks to prevent erosion, lagoons, cliffs, and mangrove swamps.

[114] The island's tropical forest and marine habitats are home to crustaceans and cetaceans in the Singapore Strait and land animals.