Colo. Rev. Stat. § 30-5-111
So much of the counties of Bent and Elbert as is included within the following described boundaries, shall be set apart and is hereby established as a county, with the legal capacity and functions of other counties of this state, to be called the county of Cheyenne:
Beginning at a point on the eastern boundary line of the state of Colorado, where the same is intersected by the line between townships numbered eleven and twelve south; thence west on said township line to the west side of range fifty-one, west of the sixth principal meridian; thence south on said range line to the township line between townships numbered sixteen and seventeen south; thence east on said township line to the eastern boundary line of the state of Colorado; thence north on said state line to the place of beginning.
C.R.S. § 30-5-111