My son (MI resident) received 1099-NEC for his internship while studying in IL. Now graduated and working in IL, W-2 employee. How should he file state taxes?

Should he file a MI tax as a part-time resident (Jan ~May) and report 1099-NEC , AND IL tax as a part-time resident (June ~ Dec) reporting W-2 income?  Which state should he report 1099-INT & Div?  Split them half?