Help! First late rent

[John Warren]

Hello everyone!

My wife and I closed our first deal on the 7th on our new four unit property which is fully occupied. One of the tenants is a co-worker, which was not something I was terribly excited about initially, but the deal was good so now he is my tenant. His rent was the first due, and it was supposed to be in yesterday (May 15th). I checked the p.o. box at midnight (I know, excited new investor right!) and there was no rent check. 

My questions is, what would you all do? Should I call him first thing this morning and just talk to him, or should I serve a five day notice right away? I was obviously hoping this wouldn't come up immediately! The building is located in cook county, Illinois by the way, so it is not a terribly land lord friendly area.