No people were injured when the 2-pound piece hit the Jefferson Township home about 2 1/2 miles from the Picatinny Arsenal and landed in the girl's bed, said Peter Rowland, arsenal spokesman. She wasn't home, but her cat was sleeping on the bed.
The homeowner told authorities she heard a loud noise around 2:40 p.m. and found the 6-by-4-inch object.
Picatinny officials told The Star-Ledger of Newark they were investigating. The base had been conducting tests Friday, and it wasn't immediately clear what type of artillery hit the home.
Picatinny is the site of the Armament Research, Development and Engineering Center, whose mission is to conduct research, development and engineering for weapons systems.