The Illinois Department of Public Health said this is the first rabid dog in Cook County since before 1964.
The agency said the dog bit someone on Dec. 11, and testing revealed it to be rabies positive.
However, the dog had been vaccinated for rabies in June.
According to the IDPH, the dog was sent to Chicago from a Florida rescue group in May, before being adopted.
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The IDPH said the dog had behavioral issues throughout its life and was euthanized on Dec. 18.
The source of rabies exposure is under investigation, and the lot of the rabies vaccination the dog received is being tested.
PAWS Chicago said it received the dog as a puppy in May, and he received various vaccines, including rabies, when age appropriate.
He was adopted into a family in July, and returned to to PAWS in December.
The organization said no PAWS animals or volunteers were in contact with the dog in December, when the virus was likely shedding.