In-state tuition status for military dependents was made effecting in all states under the Higher Education Act in 2008.
Here’s the most pertinent part of the law, the Higher Education Opportunity Act:
“In the case of a member of the armed forces who is on active duty for a period of more than 30 days and whose domicile or permanent duty station is in a State that receives assistance under this chapter and part C of subchapter I of chapter 34 of title 42, such State shall not charge such member (or the spouse or dependent child of such member) tuition for attendance at a public institution of higher education in the State at a rate that is greater than the rate charged for residents of the State.”