The John G. Diefenbaker Building is a building in the New Edinburgh neighbourhood of Ottawa, Ontario. The building served as Ottawa's city hall from 1958 to 2000, and is commonly known as Old City Hall. Purchased in 2003 by the Government of Canada, it was known by its municipal address, 111 Sussex Drive, until September, 2011 when it was renamed after Canada's 13th prime minister, John Diefenbaker.