The owner reported a large cat on the property Wednesday, and the IDNR officer found the animal in a tunnel underneath a corn crib, WREX, Rockford, Ill., reported.
After the farm owner requested the animal be euthanized, the officer checked with IDNR law enforcement and wildlife officials and then used an IDNR-issued rifle to kill the cat.
The report said the cougar looked to be about 6 feet long and weighed more than 100 pounds.
There have been at least three other confirmed cougar sightings in Illinois since 2002. The state has been mostly cougar-free since at least 1870, but the big cats have appeared from time to time -- most likely coming to the state from South Dakota and other states west of Illinois, the report said.