In general, students from Michigan pay resident tuition rates, students from outside of Michigan pay non-resident tuition rates.
Northern, like the other public universities in Michigan, charges lower tuition rates to Michigan residents, their spouses and children partially because the state universities receive some operating funds from the State of Michigan.
In most cases, if you have lived in the state of Michigan for at least six consecutive months before the first day of classes, you'll qualify as a Michigan resident. Of course, there are always exceptions.
In determining a person's eligibility for residency, each case is considered separately. Non-resident students can apply for a change in residency status by submitting a student residency application. New students should submit this form to the Admissions Office. Currently enrolled students should submit the form to the Registrar's Office.