Jeep didn't put any sensors in the front bumper or grill because of how common it is for people to mount accessories in that area. They figure the top middle of the windshield is the least likely spot for them to be blocked and rendered useless.
I just double checked on mine and there are no sensors on the bumper or the grille.
The sensors/camera that is o front and above the rear view mirror contains all of them. The Jeep also comes with a protective cover for this that you should put on if/when you have the windshield down and open.
To clarify what was said above, the sensors are in a box that is mounted on the frame of the jeep. They are not attached to the windshield. So if you drop the windshield, you're supposed to put a cover over the box so the sensors don't get dirty. (The cover comes with the jeep).
Great!! Thanks for the info. We are going to an Aluminum Patriot Mid-width flat towable front bumper on the diesel JL when it comes in. I noticed a thread about the LOD rear bumper having sensor holes in it and wondered if they were needed up front.