Which country officially founded the United Nations in 1945?

No single country founded the United Nations; 51 countries founded it together in 1945.

The organization grew out of Allied wartime cooperation during World War II. Representatives from 50 countries met in San Francisco in 1945 to draft and sign the United Nations Charter. Poland signed later, bringing the number of original founding members to 51.

The Charter was signed on 26 June 1945 and entered into force on 24 October 1945, now observed annually as United Nations Day. The UN replaced the League of Nations, which had been created after World War I but could not prevent the Second World War.

The United States, the United Kingdom, China, France, and the Soviet Union played leading roles and became the five permanent members of the Security Council. Their prominence sometimes leads to the mistaken idea that one of them founded the UN alone, but the organization's legal foundation was a multinational charter.