She is Ellys Martinez of the Bronx, New York.
It happened around 2 p.m. at the Yogi Bear Jellystone Park in Elmer, New Jersey.
Police say the girl was in her tent when she was struck by a tree branch.
She was transported to an area hospital where she later died.
The campground is known for its many mature trees.
Its website features images of several swimming pools and adjacent play areas. The resort calls itself a "fun family escape."
It reportedly has 265 campground sites and features cabins as well as locations for RVs and tents.
The park is one of several campgrounds owned by a Florida-based firm Adventure Bound Camping Resorts. Efforts to speak to someone with the company have not been unsuccessful.
It's still unclear if Saturday's severe weather contributed to the incident.