Over 50% of undergraduate students live on campus. Most of the residence halls on campus are located on the South 40, named because of its adjacent location on the south side of the Danforth Campus and its size of 40 acres (160,000 m2). It is the location of all the freshman buildings as well as several upperclassman buildings, which are set up in the traditional residential college system. All of the residential halls are co-ed. The South 40 is organized as a pedestrian-friendly environment wherein residences surround a central recreational lawn known as the Swamp. Bear's Den (the largest dining hall on campus), the Habif Health and Wellness Center (Student Health Services), the Residential Life Office, University Police Headquarters, various student-owned businesses (e.g. the laundry service, Wash U Wash), and the baseball, softball, and intramural fields are also located on the South 40.

What percent of undergraduate students live on campus at Washington University?