you need to read that link vi_edit put up. at first glance, they define resident as someone who lives in the state for any reason except for education.
also, some law students got screwed on this. they tried to declare residency after being at the school for a year, but because they were still claimed as a dependent by their parents for part of the year prior, they were not considered independent and away for the period of one year, and were denied residency status. this was of course, california, so it may vary from state to state.
"B. In order to be classified as a resident for purposes of admission, an independent person shall be domiciled in Illinois and a bona fide resident for at least one calendar year immediately preceding the date of receipt of the application for admission. To be considered a resident for purposes of assessment of tuition, an independent person must be a bona fide resident for at least one calendar year immediately preceding the first scheduled day of classes for the term for which residency is sought."
O. Exclusive use of the Illinois address when home or mailing address is requested.
looks like you can't use the dorm address.