You became an IL resident, in June, when you started living in your parent's apartment. Prior to that you were a CA resident, not an IN resident, because you were your parent's dependent prior to graduation and the move to IL.
Q. At what point could I realize a gain and only owe IL state tax?
A. The date in June when you started living in IL.
Q. Would I owe CA state tax at all on the gain I realized in January?
A. Yes.
Q. My understanding is that once I am considered an IL resident, I would only owe IL (and not CA or IN) state tax on any capital gains. Is this true?
A. Yes
