The levels of radiation are far lower than what people get from an X-ray at the doctor's office or when traveling in an airplane. Still, officials in Illinois are stepping up their testing.
In the past week, air monitors at the Argonne National Laboratory near Darien have detected elevated levels of radiation. The machines sound like a giant vacuum cleaner and act like one too, taking in air and collecting particles in filters which are then tested.
The question is, should people be worried?
"Not at all. This is miniscule amounts. And I don't really think people should worry about that," said S.Y. Chen, Argonne environmental engineer.
Scientists are certain the radiation is from Japan because of the nature of the material. The isotope is called radioiodine 131, a unique byproduct of nuclear fission with a relatively short half life, which means it had to have come from a recent event.
Argonne scientists are not surprised the radioactive materials turned up in Illinois.
"The radioactivity detected was transported by winds and jet streams," said Chen.
Low levels of radiation have also been found in air and grass samples near the Dresden Nuclear Power Plant in Will County, though officials confirm it's not from the plant itself.
The material was found during pre-scheduled testing and the Illinois Emergency Management Agency says it's expanding its monitoring to include areas far from any nuclear site.
"That will be more definitive that it's from Japan, because it wouldn't be in any area where there would be the possibility of finding the radioactive iodine," said Patti Thompson, Illinois Emergency Mgmt Agency.
The trace amounts of radiation have also turned up in rain water in other parts of the country. Scientists are awaiting the results of water testing at five sites in Illinois, though any potential levels are expected to be safe.
"It's 200,000 times lower than what the regulatory limit for releases from a nuclear power plant would be," said Thompson.
The Food and Drug Administration says tiny amounts of radiation have even turned up in a sample of milk from Washington state. Still, the levels are far below what's considered unsafe Even if the situation in Japan worsens, radiation in Illinois would remain low.