Colo. Rev. Stat. § 20-1-302
Except as otherwise specifically provided, the district attorneys of each judicial district in the state of Colorado shall be entitled to collect and receive at the end of each month, of and from the respective counties in the district attorney's judicial district, the necessary expenses of maintaining an office for the transaction of official business, which expenses shall be borne by the various counties in the judicial district, each in the proportion that the population of such county bears to the population of the whole judicial district, according to the last preceding population estimate that is prepared before May 1 of the current year by the division of planning in the department of local affairs pursuant to section 24-32-204, C.R.S. With the agreement of all of the boards of county commissioners of the judicial district, the funding allocation provisions of this section may be modified. Nothing in part 2 of this article or this part 3 shall prohibit any municipality, county, or government entity from agreeing to fund programs, projects, personnel, or salaries that are in addition to the funds provided for the reasonable and necessary expenses of the district attorney with the agreement of the relevant board of county commissioners.
C.R.S. § 20-1-302