Which is the latest country joined in UN?

Switzerland, in 2002. Switzerland last voted on UN entry during the Cold War in 1986 when the issue was defeated by 75% of voters. People feared that freedom and the rights would be limited, and neutrality would be deeply damaged. Joining UN would mean its traditional stance of neutrality would be compromised - in the event of Swiss troops being asked to be part of peacekeeping forces or asked by the Security Council to take up arms in foreign conflicts.