A.T. Still University is a private medical school based in Kirksville, Missouri, with a second campus in Arizona and third campus in Santa Maria, California. It was founded in 1892 by Andrew Taylor Still and was the world's first osteopathic medical school. It is accredited by the Higher Learning Commission. ATSU includes three campuses on 200 acres …A.T. Still University is a private medical school based in Kirksville, Missouri, with a second campus in Arizona and third campus in Santa Maria, California. It was founded in 1892 by Andrew Taylor Still and was the world's first osteopathic medical school. It is accredited by the Higher Learning Commission. ATSU includes three campuses on 200 acres with seven schools and colleges.