Apartments near Texas State University are in all directions. With a good bus system, all of San Marcos is within reach of TXST campus. With roughly 80% of TXST's 35,000 students living off campus there is a fairly high demand on housing. You will find the latest and greatest student apartment communities to the East of campus, and more traditional communities closer to campus. Relative to other Universities there are fewer apartment choices within walking distance to class.
Then again, TXST has a great bus system, with most routes stopping in the heart of campus, The Quad.