South Sudan was the last country to join the United Nations. It is the newest sovereign state in the world, and joined the organization in 2011.
Updated in 2018:
South Sudan was the last country to join the United Nations on July 14, 2011
The athletes from China will be the last to enter during the opening ceremonies. Olympic protocol dictates that the host country's athletes enter last at the opening ceremony.
According to Olympic tradition, the athletes from Greece are the first to enter the stadium and the athletes from the host country are the last to enter the stadium.
In the opening ceremony, the athletes from the host country enter last. In the closing ceremony, the athletes enter en masse and there is no structure as to what country's athletes enter last.
Greece is always the first to enter. The country that is hosting the Olympics is the last to enter
New York September 2012
453,541,589,654 years
2002
America
Mongolia, finally announced its support for the Allies on August 9, 1945. This was after the use of atomic weapons in Japan. There were many neutral nations that joined the Allies as the war was coming to a close. For a complete list of participants see; http://en.wikipedia.org/wiki/Participants_in_World_War_II
first and last
Zimbabwe
The last entrant to the UN was in 2006, so all of them - 192 members.