Presumably, way back in time, no-one owned land. (Nomadic tribes/herdsmen going where the food was). Also presumably, the next step was land-grabbing - as in “you step on my land, and I’ll do you serious damage”. Then it all settled down into what we have today: legal ownership.
What I’d like to know is - at some point, there must have been one last piece of land that wasn’t owned. When was that, and where was it? To keep this simple (ish), let’s restrict this to the USA and UK.
Well, what’s “ownership”? The Amerinds (mostly) didn’t consider land to be “owned” but they (again, mostly) used more the concept of “right to use”. Nomand tribes may not have thought much about “ownership” per se, but they did have fights & squabbles over which tribe got to use the land (hunting rights and so forth).
I know it’s outside your purview, but by & large, Antartica isn’t “owned”.
For the US, for the original territory it was pretty much whenever the colonial governments were set up and laid claim these regions. For the area of the present United States, it was whenever the federal government obtained legal jurisdiction over the component territories. The last area obtained was Hawaii in 1898. (Of course, non-private land in Hawaii may have been legally owned by the kingdom before that date.) Note that a lot of land in the US even today is owned by the federal government rather than private individuals or entities.
It depends what the meaning of “own” is.
Most European colonies in the Americas were established under some sort of royal land grant or charter under which colonists would gain rights of ownership in return for a promise to settle and improve the land. Did the land become “owned” the moment such a charter was issued? Or when the land was actually settled? Since European governments granted such charters, does that imply that they owned the land first? How could they own something they had never seen? But if they didn’t own it, how could they grant it to one of their subjects? You see the ambiguities here.
Cecil’s column on the Arabia “Neutral Zones”, one of which was “unowned” until 1981.
Hmm. In England, at least, to find some land that wasn’t nominally owned by somebody, either an individual or the state, you’d have to go back to at least 500 AD, before the “Heptarchy” of kingdoms that were combined into England by Alfred the Great came into definite existence, and probably to well before the Roman conquest in 43 AD. There hasn’t been any land in England that you could just say “This is mine now!” without being prepared to fight or pay for it for at least 1500 years, and probably quite a bit longer.
Wales is similar, the traditional mediaeval kingdoms being reasonably well-established soon after the Roman departure from Britain in 400 AD.
The history of Scotland in Roman and post-Roman times is less well-documented, but we can put a hard upper boundary at 843 AD, the (traditional) date of the foundation of the Kingdom of Alba under Kenneth MacAlpin, and the Pictish kingdoms before him can be dated back to the 3rd century AD.
I’m afraid my knowledge of American land ownership is mainly from Western movies. 
In those, the pioneers travelled west, got somewhere, stopped and said “this is mine”. It does seem rather simplistic, but did it happen this way? And so, at one point, there must have come a time when everyone had said “this is mine”, or the state had laid a claim, and there had to be one last plot that someone ‘took’. Or am I way out?
At least in Australian legal theory, all the land in each of the colonies was owned by the British Crown at the point of establishment of the colony, and the ownership later get transferred to the Crown in right of the state that developed from the colony. When land is acquired compulsorily by an Australian state (what’s called “eminent domain” in the US), it’s called resuming the land, because the Crown always used to own the land at some point in time.
(This is related to the “terra nullius” doctrine, and has been mitigated to a certain extent by the recognition of native title, i.e., ownership that can be traced back to the people who occupied the land before colonisation.)
The US Homestead Act was repealed in 1976, and the last homesteader was Kenneth Deardorff, who filed a homestead claim on 80 acres of land on the Stony River in southwestern Alaska.
Of course, you could argue the lasnd was owned by the US government, but it is a milestone in the timeline of the ownership of the earth.
As an aside, in Panama one can still in effect obtain government land by staking a claim to it. A small farmer can establish derechos possesorios (rights of possession, essentially “squatter’s rights”) to a plot of land by clearing it and filing a claim with the Agricultural Reform Agency. These rights can eventually be converted to formal title by paying a fee.
At certain times and places, you could pretty much do that. Under homesteading, you could just stake your claim. Even before homesteading, sometimes you could just squat–if you were lucky and didn’t get chased off or killed, after a period of years you might establish ownership by right of possession and courts would recognize it. (Courts weren’t always sympathetic to big land companies trying to enforce nebulous claims under old royal and colonial grants.)
But even under those conditions, it’s hard to argue that nobody owned the land before. Under homesteading, the federal government owned the land (which they bought from France, Mexico, or Russia), and they chose to allow homesteading. If you were squatting, it was more ambiguous, but you were still squatting on somebody’s land–if a land company’s title was invalid, then the state government owned the land and they might choose to honor squatter’s rights.
It would be interesting to know when the last successful “squat” was (no bathroom jokes please!). For all I know, there may be places where you can still get away with it today.
If I understand current landlord-tenant law, ‘right to use’ can be completely separated from ‘ownership’, in the sense that the lessor largely abjures the right to enter the property, except in special circumstances. So the tenant has the right to use, and the landlord has the ownership.
Two concepts often confused:
Terra Nullius. Which is land that is not claimed by any sovereign. http://en.wikipedia.org/wiki/Terra_nullius
Land subject to claim by by individuals with permission of the sovereign. Individuals can only claim property in a country’s territory under the established real property regime of that sovereign. It might or might not include homesteading or squatting.
There are still places in northern Canada that can be staked and claimed as your own. You need to occupy that land for a certain amount of time, but after that, it becomes your property.
Of course most of this land would be arctic tundra… Not exactly the most inviting territory around.
The OP might be interested in this article: http://en.wikipedia.org/wiki/Rockall