Singapore Island, also known as mainland Singapore, is the main constituent island of the sovereign island country and city-state of the Republic of Singapore. It is located at the southern tip of the Malay Peninsula, between the Straits of Malacca and the South China Sea. The Singapore Strait lies to the south, while the Johor Strait lies to the nor…Singapore Island, also known as mainland Singapore, is the main constituent island of the sovereign island country and city-state of the Republic of Singapore. It is located at the southern tip of the Malay Peninsula, between the Straits of Malacca and the South China Sea. The Singapore Strait lies to the south, while the Johor Strait lies to the north.