Colo. Rev. Stat. § 39-1-105
All taxable property, real and personal, within the state at twelve noon on the first day of January of each year, designated as the official assessment date, shall be listed, appraised, and valued for assessment in the county wherein it is located on the assessment date. Personal property shall be listed and valued separately from real property. Whenever construction of any new taxable building within the boundaries of a county occurs subsequent to the assessment date but before July 1 and such county has resolved to implement the procedures set out in section 39-5-132, such building shall be listed, appraised, and valued pursuant to section 39-5-132.
C.R.S. § 39-1-105
For property brought into the state after assessment date, see § 39-5-110 ; for property destroyed after the assessment date, see § 39-5-117 ; for the procedure for exclusion of property within a municipality from a special district and for the effect of such an exclusion order, see §§ 32-1-502 and 32-1-503 .