The cat lived about three miles west of Mountain Home and had contact with ground squirrels, who were recently tested plague positive, the Central District Health Department said.
The family who the cat lived with and other household pets are currently placed under observation to ensure the infection didn't spread.
The discovery of cat has expanded the area of impact for plague found in ground squirrels into Elmore County. People living in the area have been urged to exercise caution.
"This is a reminder that whether you live in the area of impact or recreate there, it is very important to take precautions to avoid contact with ground squirrels and their potentially infected fleas," Sarah Correll, epidemiologist for CDHD said.
"Make sure your pets have proper flea control. Do not let your pets touch ground squirrels in the affected area. People can be exposed to plague when pets bring infected fleas back into the home, by caring for a sick pet without proper precautions, or by contact with rodents carrying fleas."