The country with the largest population that is not a UN member is Taiwan. With more than 23 million residents, Taiwan is far more populous than other commonly cited non-member entities such as Kosovo, Palestine, and Vatican City.
Taiwan has governed itself since 1949, when the Republic of China government relocated there after losing control of mainland China in the Chinese Civil War. The island operates with its own government, military, currency, passport system, and elections, although the People’s Republic of China claims sovereignty over it.
Taiwan lost its UN seat in 1971, when the General Assembly recognized the People’s Republic of China as the representative of China. Taiwan is therefore not a UN member, but it remains a major economy and a self-governing political entity. Kosovo and Palestine are also outside full UN membership, but their populations are much smaller; Vatican City is the smallest country in the world by both area and population.