How do I know if my W2 income is from another state when I work from home?

[mikepeterson76]

My employer is headquartered in MA, but may have offices in CT. They withheld CT taxes for me, and I live in CT. How do I know if I they are regarded as a MA or CT employer? Does their State ID number reveal the answer?

[JamesG1]

Contact your employer's Human Resources department to clarify your status.

Massachusetts is not a 'convenience of the employer' state.  See here.  You should file a resident Connecticut resident income tax return and report your income.

The convenience of the employer rule applies to certain taxpayers who work from home. It means you are taxed as if you work in your employer's state even if you do not work there.