"The University of Illinois requires that you be a bona fide resident of Illinois for one calendar year prior to the term for which you are applying for resident status. The University's requirements to establish residency may be different than other Illinois institutions of higher education or government agencies. Bona fide residency involves being gainfully employed and actually living in the state for one year, and taking other specific actions which link you to the state of Illinois. It also requires that you reside in Illinois primarily for reasons that are not related to receiving an education. Itís important that actions be completed before the beginning of the term in which you are attempting to establish residency."
"3. What is meant by gainful employment?
Gainful employment means that you earn income and file and pay taxes in Illinois on income sufficient to meet one-half of tuition, fees and normal living expenses for a one-year period. Loans from parents or support from a relative in Illinois does not constitute self-sufficiency or gainful employment, for example.
Employment during the summer terms alone does not fulfill either gainful employment or the one-year requirement."
-From the residency FAQ I linked to above...