From the Wikipedia page [1]
St George Hanover Square was a civil parish in the metropolitan area of London, based on the church of St George's, Hanover Square.
It was created in 1724 from part of the ancient parish of St Martin in the Fields, and was within the Liberty of Westminster.
It included within its boundaries the grounds of Buckingham Palace, although the palace itself was in St Martin in the Fields.
In 1855 the parish vestry became a local authority within the area of responsibility of the Metropolitan Board of Works.
In 1889 the parish became part of the County of London and in 1900 it became part of the Metropolitan Borough of Westminster. It was abolished as a civil parish in 1922.