From the Illinois Schedule CR instructions:
"Taxes that qualify for the credit are income taxes you paid to another state of the United States, the District of Columbia, the Commonwealth of Puerto Rico, or any territory or possession of the United States, or to a political subdivision (e.g., county, city, local) of one of these jurisdictions."
Also:
"A part-year resident may only take a credit on income earned while a resident of Illinois."
Thus the only qualifiers are that 1) you earn the income as a resident of Illinois; and 2) that you pay income tax on it to another state as well as to Illinois.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
