If a mountain lion is on your property and it is attacking you or your pets,livestock, etc. it is legal to shoot it. Would you be willing to fill out a report on the sighting? It can be accessed at:
http://web.extension.illinois.edu/wildlife/sightings_report.cfm
SB 3049 was passed by both houses this spring. It awaits the Governor's signature. It provides that an owner or tenant whose person or property is in imminent danger from a gray wolf, American black bear, or mountain lion may take the animal without restriction. An owner or tenant whose property is threatened, but not imminently threatened, by a gray wolf, American black bear, or mountain lion may apply to the Department of Natural Resources for a nuisance permit that shall allow the owner, tenant, or their designated agent to take the animal.