Boulder is a home rule municipality just like Denver. Here is a list - sort by the "Government" column and the home rule municipalities will jump to the top.

https://en.wikipedia.org/wiki/List_o...ns_in_Colorado

Colorado has 61 cities and 35 towns that are home rule municipalities:

Colorado home rule municipalities are self-governing under Article 20 of the Constitution of the State of Colorado; Title 31, Article 1, Section 202 of the Colorado Revised Statutes; and the home rule charter of each municipality. The home rule charter determines the form of government. A Colorado home rule municipality may declare itself to be either a city or a town.