Actually, the number is 13 which is clearly not 'most'.
State Actions
In June 2001, Texas (HB1403) was the first state to pass legislation allowing in-state tuition for immigrant students, followed by California (AB540), Utah (HB144), and New York (SB7784) in 2001-2002; Washington (HB1079), Oklahoma (SB596) and Illinois (HB60) in 2003; Kansas (HB2145) in 2004; New Mexico (SB582) in 2005; Nebraska (LB239) in 2006; Wisconsin (A75) in 2009; Maryland (S167/H470) and Connecticut (H6390) in 2011.
States that have barred unauthorized immigrant students from in-state tuition benefits include Arizona (Proposition 300, 2006), Colorado (HB 1023, 2006), Georgia (SB 492, 2008), South Carolina (HB4400, 2008), and Indiana (H 1402, 2011).
I think that if you research you will find that states that don't address it specifically in their laws, give the instate tuition rate to students who reside in their state, no matter what their status is. So, the number becomes most, not thirteen. Check it out, I think it's right there on the linked page.
FWIW, Numbers usa is not a pro immigration website.