What the partnership pays (if they do it correctly) is an estimated tax. You must then file a PERSONAL tax return in the state to reconcile your taxes. The business cannot know exactly what your personal taxes will be. You do NOT need to file a partnership IL return, but you do need to file a state tax return - regardless of if the partnership paid your tax or not.
It's just like when an employer withholds income taxes from your paycheck, it is reconciled at year end when you file for April 15th.
