I seem to be in quite a pickle. I moved into an apartment in Chicago, IL seven and a half months ago (10/01/2008), alone. I paid a security deposit equal to one month's rent, and I never actually signed a written lease with the landlord. After three and a half months (mid-January, 2009), I invited a friend to move into my spare bedroom with my landlord's permission. So neither of us have a written lease neither with the landlord nor with one another. Furthermore, we both write checks for our respective shares of the rent directly to the landlord.

When I try to find applicable advice online, I frequently find information about serving a Termination of Tenancy giving the other one full rent period to vacate the property (30 days, I believe, for Chicago) because without a written lease, we are technically month-to-month tenants. I also find information regarding sublandlord/subtenant situations, but I think I might be in a different situation given that neither I nor the roommate has his name on a written lease.

The roommate and I have had a falling out and I wish no longer to live with him. To clarify, this is strictly a matter of personal differences and not a circumstance of one party not paying rent or utilities on time, etc. I know that changing the locks or throwing his personal belongings out the window are illegal and not the proper way to approach a legally sound solution to the matter.

My question really boils down to this: what are my options? Do either I or the actual landlord have the legal power to serve just one person in the apartment a Termination of Tenancy notice? In this case, it would be the unwanted roommate, as I have spoken with my landlord and he believes this is technically "my apartment" and that if I want to kick my roommate out, he is OK with that... but I know that his permission is not necessarily legal protection for me.
On the other hand, what rights do I have if I were to leave instead? Can I give the landlord (and my roommate) 30 days' notice to move out and legally terminate my lease altogether with no outstanding obligations? This would obviously mean that my current roommate would assume all responsibility for the apartment, including my current share of the rent. If I were to take this method of action, I would also like to recover my security deposit as well, (and the roommate never paid a security deposit since he moved in with me later... ).

I will greatly appreciate your advice concerning my situation. I have learned the importance of written lease agreements, that's for sure! :) Thank you.

Since you and your roommate pay rent separately to the landlord I would say that both of you are month-to-month tenants under the landlord, rather than being a sublandlord/subtenant situation. So your landlord would have to terminate your roommate's tenancy.

On the other hand, you can terminate your tenancy with 30 days written notice. Since the landlord does not have a written agreement with you I can't see how the landlord can withhold your security if your roommate doesn't move out as well. But if the landlord persists in thinking that this is "your apartment" then you may have to sue the landlord to get your deposit back.

I go along with Lisa's response here. Since you went to the landlord and informed him of the new occupant and since he pays his rent directly to the landlord, then he is a tenant of the landlord, not you.

This means that the landlord would have to terminate his tenancy. You cannot. But it also means you can choose to move, giving proper notice and get your security back.