In the United States, is there any land anywhere that isn’t owned by anyone? Does the local or federal government automatically own any land that isn’t privately owned?
The government owns all lands not in private hands by default. They used to sell or give some of this land to people (for example: the Homestead Act), but apparently no more. See the history of the BLM here:
I forgot to say, the among other duties, the Bureau of Land Management administers government land that hasn’t been designated for other uses.
There are thousands of acres, in fact thousands of square miles, of land that is administered by the Bureau of Land Management (Department of the Interior) and the US Forest Service (Department of Agriculture) in the Sierra Nevada range and on the desert in California where I live. And that doesn’t include places like Yesemite, Sequoia, Death Valley National Parks.
Canada also has land available. In some cases it will help if you are a Native American. Also I doubt if all of Siberia has been spoken for.
Bureau of Land Management (BLM) - 261 million acres
USDA Forest Service - 192 million acres
DOI National Park Service - 79 million acres