This article shall apply only to those counties which have a population of 500,000 or more according to the United States decennial census of 1990 or any future such census and to those municipalities wholly or partially located within such counties which have a population of 100,000 or more according to the United States decennial census of 1980 or any future such census. As used in this article, the term "local government" means those counties and municipalities subject to this article; and the term "governing authority" means the governing authority of each such county and municipality.