The United States has income tax treaties with a number of foreign countries. Under these treaties, residents (not necessarily citizens) of foreign countries are taxed at a reduced rate, or are exempt from U.S. income taxes on certain items of income they receive from sources within the United States. These reduced rates and exemptions vary among countries and specific items of income. See Publication 519, U.S. Tax Guide for Aliens, and Publication 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.
Many of the individual states of the United States tax the income of their residents. Some states honor the provisions of U.S. tax treaties and some states do not. Therefore, you should consult the tax authorities of the state in which you live to find out if that state taxes the income of individuals and, if so, whether the tax applies to any of your income, or whether your income tax treaty applies in the state in which you live.
The State of Illinois honors the provisions of U.S. Tax treaties.