C.R.S. § 31-1-201

(1) With respect to the exercise of corporate and municipal powers, the municipalities of this state are divided into the following classifications: (a) Cities or towns incorporated prior to July 3, 1877, which have retained such organization; (b) Cities or towns organized pursuant to the provisions of article XX of the state constitution; (c) Cities and towns organized pursuant to the provisions of this title or of any other general law on or after July 3, 1877, which have not chosen to adopt a home rule charter under the provisions of article XX of the state constitution.