Illegally manufactured Mexican-style cheese has been linked to around 100 cases of Salmonella.
The average age of people who have become ill is nine and a third of the cases have been hospitalized.
Illinois Department of Public Health (IDPH) said 13 counties were affected.
Many cases have reported consuming Mexican-style cheese from worksites, including factories, and at train stations, from street vendors and from relatives and friends.
The cheese is not labeled and is often wrapped in aluminum foil.
A sample from the home of a person who became ill tested positive for Salmonella.
Cases since July 2012
Local health departments have reported to IDPH since July 2012 around 100 cases with the same strain of Salmonella believed to be associated with the cheese.
IDPH is working with local health departments to identify the manufacturer of the contaminated cheese.
Dr LaMar Hasbrouck, IDPH director, said it was concerned that people who consume the manufactured cheese may become sick from Salmonella.
“It is important for you to check the labeling to make sure the product was made by a licensed dairy manufacturer - even if you purchased the cheese from a grocery store.
“If you become ill after eating Mexican-style cheese, contact your health care provider and your local health department.”
In Illinois about 1,500 to 2,000 cases of Salmonellosis are reported each year
IDPH recommended that people who have Mexican-style cheese in their home, but cannot clearly identify the product was made by a licensed or regulated manufacturer, should not eat it.
People who become ill after eating illegally manufactured cheese, should keep it for possible testing.
The agency advised against buying or consuming cheese that is suspected to be made by an unlicensed dairy manufacturer.
“Legitimate Mexican-style cheeses are available in the refrigerated case at retail stores and in most cases, label information specifies the legal name of the product, the name and address of distributor or processor, quantity of contents, an ingredient statement, and nutrition facts,” said a statement.