Answer: The federal government owns roughly 640 million acres, about 28% of the 2.27 billion acres of land in the United States. Four major federal land management agencies administer 606.5 million acres of this land (as of September 30, 2018). They are the Bureau of Land Management (BLM), Fish and Wildlife Service (FWS), and National Park Service (NPS) in the Department of the Interior (DOI) and the Forest Service (FS) in the Department of Agriculture. A fifth agency, the Department of Defense (excluding the U.S. Army Corps of Engineers), administers 8.8 million acres in the United States (as of September 30, 2017), consisting of military bases, training ranges, and more. Together, the five agencies manage about 615.3 million acres, or 27% of the U.S. land base. Many other agencies administer the remaining federal acreage.
Explanation: Pursuant to the Property Clause of the United States Constitution (Article 4, section 3, clause 2), the Congress has the power to retain, buy, sell, and regulate federal lands, such as by limiting cattle grazing on them.