Required notice for MTM tenant in Berwyn, IL

[Phil Kagebein]

I'm purchasing a 3-flat in Berwyn soon, with all three units occupied on month-to-month leases. I plan on living in one of the units and I know I need to give the tenant a 30 day notice to move out. Just wondering if I can request they leave in middle of the lease and I return prorated rent, or if I have to wait until the lease is over. 

Hypothetically if I closed today and their lease ends on the 31st of July, can I request they leave by July 16th? Or do I have the wait until the lease ends? 

Thanks!