This report, sponsored by the Illinois Board of Higher Education and the Center for the Study of Education Policy at Illinois State University, presents in-depth multi-method research and analysis on what matters to Illinois students and their families when choosing a college, why so many students are leaving the state, where they are going, and what the state might do to encourage greater retention. The study shows that the highest concentrations of Illinois student migrants only go as far as adjacent states, accounting for nearly half of all student migrants. Their rationales behind this migration--detailed in this report--have implications for the affordability, quality, selectivity, distribution, capacity and marketing of Illinois colleges and universities. The report presents recommendations for the Illinois Board of Higher Education, the Governor and Legislature, colleges and universities, and high school guidance counselors. Appended are: (1) Independent Variables Used in Migration Trend Analysis, IPEDS (Integrated Postsecondary Education Data System); (2) Institutional Characteristics of Colleges and Universities Enrolling the Highest Numbers of IL Student Migrants, Fall 2004 Freshman Class; and (3) Type, Size and Selectivity of Colleges and Universities Enrolling the Highest Numbers of IL Student Migrants, Fall 2004 Freshman Class. (Contains 13 figures, 3 tables and 11 notes.) [This study was supported by a Higher Education Cooperative Act grant from the Illinois Board of Higher Education.]