Colo. Const. art. XIV, § 6

County commissioners - election - term. In each county having a population of less than seventy thousand there shall be elected, for a term of four years each, three county commissioners who shall hold sessions for the transaction of county business as provided by law; any two of whom shall constitute a quorum for the transaction of business. Two of said commissioners shall be elected at the general election in the year nineteen hundred and four, and at the general election every four years thereafter; and the other one of said commissioners shall be elected at the general election in the year nineteen hundred and six, and at the general election every four years thereafter; provided, that when the population of any county shall equal or exceed seventy thousand, the board of county commissioners may consist of five members, any three of whom shall constitute a quorum for the transaction of business. Three of said commissioners in said county shall be elected at the general election in the year nineteen hundred and four, and at the general election every four years thereafter; and the other two of said commissioners in such county shall be elected at the general election in the year nineteen hundred and six and every four years thereafter; and all of such commissioners shall be elected for the term of four years. This section shall govern, except as hereafter otherwise expressly directed or permitted by constitutional enactment.