9Niihau Island, Hawaii, USA

Also known as the Forbidden Island, Niihau was purchased by Elizabeth Sinclair, a Scottish farmer and plantation owner, back in 1864 and since then it’s privately owned by her descendants.
In 1952, the Hawaiian islands faced a polio epidemic and, as an attempt to avoid the spreading of the disease, a ban to leave or enter the island was issued. Luckily, no one got sick on Niihau and now it houses a population of only around 170 people.