In the United States governmental entities including cities, counties, states, and the federal government all manage land which are referred to as either public lands or the public domain.
The majority of public lands in the United States are held in trust for the American people by the federal government and managed by the Bureau of Land Management (BLM), the United States National Park Service, Bureau of Reclamation, or the Fish and Wildlife Service under the Department of the Interior, or the United States Forest Service under the Department of Agriculture. Other federal agencies that manage public lands include the National Oceanic and Atmospheric Administration and the United States Department of Defense, which includes the U.S. Army Corps of Engineers.
In general, Congress must legislate the creation of new public lands, such as national parks; however, under the 1906 Antiquities Act, the President may designate new national monuments without congressional authorization.
Each western state also received federal "public land" as trust lands designated for specific beneficiaries, which the States are to manage as a condition to acceptance into the union. Those trust lands cannot any longer be considered public lands as allowing any benefits to the "public" would be in breach of loyalty to the specific beneficiaries. The trust lands (two sections, or about per township) are usually managed extractively (grazing or mining), to provide revenue for public schools. All states have some lands under state management, such as state parks, state wildlife management areas, and state forests.
Wilderness is a special designation for public lands which have been completely undeveloped. The concept of wilderness areas was legislatively defined by the 1964 Wilderness Act. Wilderness areas can be managed by any of the above Federal agencies, and some parks and refuges are almost entirely designated wilderness. A wilderness study area is a tract of land that has wilderness characteristics, and is managed as wilderness, but has not received a wilderness designation from Congress.
Typically each parcel is governed by its own set of laws and rules that explain the purpose for which the land was acquired, and how the land may be used.