The Assessors Personal Property staff takes the information provided by the taxpayer and calculates a value for each business; a Notice of Valuation is mailed by June 15. If you have also filed a paper declaration, please note that on your online form. The Assessor is located at 1325 Pearl St. Courthouse, Boulder on the Pearl Street Mall. The mailing address is: PO Box 1759, Boulder, Colorado 80306.