Believe it or not, it's Arkansas, with a 48.7% acceptance rate for IS applicants. (One school, accepts 48.7% of the IS applicants who apply.) Also way up there are Mississippi, North and South Dakota, Oklahoma and Vermont, each with a 30% plus acceptance rate for IS residents to their IS school(s). That's measured per school.
Texas has a reputation for unusually high acceptance rates because state law requires public schools to award 90% of their spots to IS residents , but there are a lot of applicants for those seats, so the average per-school IS acceptance rate is one of the lowest (rank 42) at 5.9%. (Of IS applicants to each school, an average of 5.9% are accepted.) However, added together across all schools, about 36% of IS applicants who apply IS get admitted somewhere IS. (Typically, Texas residents apply to almost all of the IS programs.)