The University of Illinois at Urbana–Champaign (U of I, University of Illinois, UIUC, or simply Illinois) is a public research-intensive university in the U.S. state of Illinois. A land-grant university, it is the flagship campus of the University of Illinois system. The University of Illinois at Urbana–Champaign is the second oldest public university in the state (after Illinois State University), and is a founding member of the Big Ten Conference. It is a member of the Association of American Universities and is designated as a RU/VH Research University (very high research activities). The campus library system possesses the second-largest university library in the United States and the fifth-largest in the country overall, after the Library of Congress, the Boston Public Library, Harvard University Library, and New York Public Library.
The university comprises 17 colleges that offer more than 150 programs of study. Additionally, the university operates an extension that serves 2.7 million registrants per year around the state of Illinois and beyond. The campus holds 647 buildings on 4,552 acres (1,842 ha) in the twin cities of Champaign and Urbana (together known as Champaign-Urbana); its annual operating budget in 2011 was over $1.7 billion.