Any county or municipality adjacent to an area under the jurisdiction of a regional planning commission may be included in such regional planning commission by agreement between its board of county commissioners, or governing body, or in charter cities the officials having charge of public improvements and the governing bodies which are members of the regional planning commission. Any such county or municipality, upon being included in the regional planning commission, shall be subject to all provisions of this part 1 relating to regional planning commissions.
C.R.S. § 30-28-129