What is a state ID number?

A state ID number (also known as a state EIN, a state employer ID, or a state tax registration) is a unique number assigned by the state to all the businesses or organizations operating in that state and is used for filing taxes.

So, when declaring the income and withholdings for a state, the employer's State ID number is required. You can find this information in the letter you received from the state’s department of revenue while registering your business. 

Click here to learn more about the states that mandate state ID number