The former student, who was not identified, has meningococcal meningitis, a contagious and potentially lethal brain or spinal inflammation, university spokeswoman Robin Kaler said.
Campus officials are investigating the possibility the cases are related, she said.
"The doctors at McKinley are exploring any potential connection," Kaler said, referring to the on-campus McKinley Health Center.
Roughly 30 students believed to have been in close contact with the recent graduate have been contacted and are expected to be treated at the health center with the antibiotic Cipro, Dr. Robert Palinkas, the director of the health center, said in a news release.
The drug is 100 percent effective in treating patients who haven't shown any symptoms of the disease -- high fever, stiff neck and headache -- the doctor said.
The student hospitalized Feb. 20 was released this week and is expected to fully recover, Kaler said.
Another student, 21-year-old Robert Davis, died last week in a Joliet hospital of an unknown ailment. Contagious meningitis was ruled out. The Will County coroner's office did not immediately return a call Thursday from The Associated Press about his autopsy results.
Kaler couldn't recall a series of meningitis cases on the Illinois campus since the early 1990s.
Five students died of the illness and another eight were hospitalized between February 1991 and April 1992. Centers for Disease Control investigators never found a link between the cases other than what they called an "interesting statistical association" and visits to crowded area bars.
University officials are putting up posters around campus advising students on ways to avoid contracting meningitis, Kaler said.
"Don't share glasses, don't share utensils, don't share a cigarette, be careful about kissing," she said. "Those are the ways this is spread."