Health experts say that this is the second cat death within the last week which is believed to be connected to the bacterial infection.
It is however notable that the cats were owned by separate families. The second cat lived both indoors and outdoors, and was in contact with ground squirrels before becoming ill.
The health experts are monitoring family members and other household pets to ensure the cat did not spread the infection.
Final lab results will be available next week.
According to Dr Mark Drew, State Wildlife Veterinarian: "We want to emphasize that plague is likely present at some level in ground squirrel populations throughout the sagebrush habitat in southern Idaho. With the known confirmed cases in these areas we want to people to be aware and be able to take appropriate steps to protect themselves and their pets from plague."