Before using the portal, your business must be registered with the Cook County Department of Revenue. If you are not sure your business is currently registered, please visit https://www.cookcountyil.gov/agency/department-revenue. Under each tax found on the right hand side of the page, the Department lists all its registered businesses. If your business is not registered and/or you have a new business, please visit www.ccdortax.cookcountyil.gov and click either “Register a new business” or “Voluntary Disclosure Program.” Once your business is registered and for those that already are, the Department will mail a letter containing a Cook ID and PIN that will be needed to create your Taxpayer Administrator portal profile.