was this headquarters built on a temporary site earlier?
Yes, at Sperry Corporation's offices
Headquarters of the United Nations
Prior to the construction of the current complex, the UN was headquartered at a temporary location at the Sperry Corporation's offices in Lake Success, New York, an eastern suburb of the city in Nassau County on Long Island, from 1946 to 1952. 
the country where the headquarters of the united nations is located New York City when was this established? 1952 who designed this building? Wallace Harrison where is he from? America can you tell me some other projects that he has worked on other than the headquarters? Rockefeller Center, Metropolitan Opera House, Empire State Plaza, United Nations complex, etc
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Headquarters of the United Nations [SEP] Previous temporary sites
In 1945–46 London hosted the first meeting of the General Assembly in Methodist Central Hall, and the Security Council in Church House. The third and sixth General Assembly sessions, in 1948 and 1951, met in the Palais de Chaillot in Paris. Prior to the construction of the current complex, the UN was headquartered at a temporary location at the Sperry Corporation's offices in Lake Success, New York, an eastern suburb of the city in Nassau County on Long Island, from 1946 to 1952. The Security Council also held sessions on what was then the Bronx campus of Hunter College (now the site of Lehman College) from March to August 1946.