The iPOD does not plug in the USB, it uses the so called UCI, but the adapter harness is an option. If not pre-installed, you need purchase and install it separately. I don't know off hand if you would need the $90 or $30 harness.. If the harness is pre-installed in your Jeep, the iPOD connector cable end should be in the glove box, check your owners manual for UCI.
Otherwise you use the aux input for audio.
2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6, 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac