There are no known cougar populations in Illinois.
While the IDNR does investigate several alleged cougar sightings each year, most if not all turn out to be a case of mistaken identity. The animals most often mistaken for cougars are coyotes, bobcats, or large domestic dogs or cats.
Actual cougar sightings in Illinois are few and far between. One confirmed sighting occurred in April of 2009 in the Chicago neighborhood of Roscoe Village. The cougar was killed by police officers and widely believed to have come from outside the state. Previously, the last sighting had been in December of 2004 in Mercer County. It was found already dead, apparently shot with an arrow.
Another cougar was found dead after it was hit by a train in Randolph County in July of 2000. Prior to 2000, the last verified record of a cougar in Illinois was from Alexander County in 1862.
In 2013, a cougar – possibly dispersing all the way from the Black Hills of South Dakota – was killed in Morrison, about 130 miles west of Chicago. In 2014, the Illinois legislature voted to add cougars (along with black bears and wolves) to the state protected species list, possibly paving the way for recolonization and increased tolerance.