720 ILCS 5/37-5

A private person may, after 30 days and within 90 days of giving the Attorney General and the State's Attorney of the county of nuisance written notice by certified or registered mail of the fact that a public nuisance as described in Section 37-1 of this Act, commence an action pursuant to Section 37-4 of this Act, provided that the Attorney General or the State's Attorney of the county of nuisance has not already commenced said action.