C.R.S. § 33-6-104

(I) Providing personal service of the copy directly to the alleged offender;

(II) Leaving the copy at the alleged offender's last-known place of residence with an individual who is eighteen years of age or older and who resides at the residence; or

(III) Mailing the copy to the alleged offender's last-known place of residence by certified mail, return receipt requested. Service by certified mail is complete upon return of the receipt signed by the alleged offender.