You must notify the Department's Registration Unit in writing if you change your business structure such as changing the structure from a sole proprietor to a partnership or corporation.  Send a letter explaining the change to:

Department of Revenue Services
Registration Unit
P.O. Box 2937
Hartford, CT 06104-2937

If you are required to obtain a new Federal Employer Identification Number (FEIN) in connection with the change in business structure, you will also be required to obtain a new Connecticut tax registration number.

For example, if your business was initially formed as a sole proprietorship and you later formed a partnership with another person, you will be required to obtain a new FEIN from the Internal Revenue Service for the partnership.  You will also have to obtain a new Connecticut tax registration number by completing Form REG-1, Business Taxes Registration Application.  You must also cancel your existing Connecticut tax registration number by following the instructions for Ending a Business.