State health officials linked the outbreak to Mexican-style cheese that's made illegally. The 13 counties affected include Cook, DuPage, Kane and McHenry.
A sample of the cheese taken from the home of a person who became ill tested positive for salmonella.
The Illinois Health Department says people should check the labeling to make sure the product is made by a licensed dairy farmer, even if it's from a grocery store.
Anyone who has become sick from eating Mexican-style cheese should call the health department.
