The boxes were constructed with a combination of steel beams and fiberglass composite material to save space.
The boxes are being delivered by FedEx and the project has been in the works for more than 10 years.
The company said it built the boxes using materials from an old construction site in Maryland, but it has not released the location.
It is the second time the company has built a FedEx box in the U.S. The first was a FedEx truck and the second was a box built in Canada.
The boxes are designed to hold three to four people.