If your service member is on active duty and stationed in Mississippi, you pay in-state tuition at Mississippi state-supported colleges and universities. You normally lose the rate when the service member is reassigned elsewhere in the continental United States, unless you began and completed your senior year of high school in Mississippi and enrolled at a Mississippi school, you stay continuously enrolled at a Mississippi school, or the service member was sent overseas after a Mississippi assignment.
Contact the admissions office at the Mississippi state-supported school you plan to attend and ask them to classify you as a resident for tuition purposes.
The service member’s orders assigning them to Mississippi, your military dependent ID, and proof of your relationship such as a marriage certificate or birth certificate.