This ID number, also known as your Illinois Tax ID Number, or your Illinois Business Tax Number is an eight digit number, usually hyphenated in the middle. This should not be confused with your Federal Employer Identification Number. The two are completely different. Locating your number is a common problem because most legal entities are not set up correctly. The attorneys can certainly set up the entity and get the FEIN, but many times they forget to set you up with the state. If neither your accountant and nor your attorney have done this, then it’s time for you to call us at 773-267-7500.