Written leases can specify whatever the parties agree to.  Unwritten ones have specific legal guidelines. 

from http://web.extension.uiuc.edu/leasingforum/i1600_582.html#1 (highlighting is by me)

Year-to-year leases that do not have a termination provision are controlled by Illinois statute. A year-to-year lease can be a written lease that states that the lease will run from one year to another year unless notice to terminate is given or it can be a verbal lease. The statute says that termination notice shall be given in writing not less than four months prior to the end of the lease year. The lease year is normally presumed to end on the last day of February. Therefore, termination notice must be given on or before the last day of October.