How Long will a credit delinquency stay on your credit report?

In August 2007, I had just finished a lease on my apartment and moved out of state. I had a roommate who I left cash to pay the final Utility bill of 195 dollars and he didn't do it. He was a good friend so I trusted him to do so. Anyways I just found out about this (They didn't have my forwarding address, I had a new phone, and the old roommate didn't bother to tell me). I just paid the 195 dollars in full and was wondering how long it would take to get off my record. It was a collection agency I dealt with and they were very rude and told me they don't know.