MORRIS, Ill. (CBS) – Five people have been taken to the hospital as a precaution after opening a letter containing an unknown white power at the courthouse in Grundy County.

Grundy County Sheriff Tery Marketti tells WBBM Newsradio that the letter arrived around noon Monday at the courthouse in Morris.

“We received notification from the judge’s office that they opened a letter that was threatening towards the judge and had a small amount of white powder inside the envelope,” Marketti said.

Five people were taken to the hospital as a precautionary measure after workers in the judge’s office opened the letter and discovered the powder.

“As a precautionary measure, the fire chief and I asked them to be sent to the hospital just to be checked,” Marketti said.

Marketti said a hazardous materials team was in the process of trying to determine if the substance is dangerous. The courthouse was still open Monday afternoon, but the third floor was closed until the letter is checked out.