This piece on my rear bumper recently disappeared. Anyone know what it is? Part number? Looks like a key hole behind it. Thanks for your help.

 

its the access cover for the spare tire hoist. Dealer will know the part number. it will be a paint to match part if you buy new. try a wrecking yard.

 

kselman, welcome to the forum...
As tech2 said, it is for the spare tire hoist. I would add that its a good idea to know how to lower the spare tire prior to needing it...
In some areas because of weather and other factors the spare tire hoist can become stuck, better to find this out now rather then on a dark highway on a cold rainy night in the middle of nowhere....
Once the cable is fully extended, hit it with some spray lubricant...